Question regarding "boot-hartid" DT node

Question regarding "boot-hartid" DT node

[Sunil V L]

Hi All,
   I am starting this thread to discuss about the "boot-hartid" DT node
   that is being used in RISC-V Linux EFI stub.

   As you know, the boot Hart ID is passed in a0 register to the kernel
   and hence there is actually no need to pass it via DT. However, since
   EFI stub follows EFI application calling conventions, it needs to
   know the boot Hart ID so that it can pass it to the proper kernel via
   a0. For this issue, the solution was to add "/chosen/boot-hartid" in
   DT. Both EDK2 and u-boot append this node in DT.

   But above approach causes issue for ACPI since ACPI initialization
   happens late in the proper kernel. Same is true even if we pass this
   information via SMBIOS.

   Do you have any suggestions what can be done in ACPI case? Can we use
   a UEFI variable with RVI specific GUID to pass this information? This
   will have the advantage that it can work with either DT or ACPI.
   Also, we may not need any UEFI spec update. Do you see any issue with
   this approach? Your inputs will be very helpful.

Thanks!
Sunil

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Re: Question regarding "boot-hartid" DT node

[Heinrich Schuchardt]

On 12/2/21 16:05, Sunil V L wrote:
> Hi All,
>     I am starting this thread to discuss about the "boot-hartid" DT node
>     that is being used in RISC-V Linux EFI stub.
> 
>     As you know, the boot Hart ID is passed in a0 register to the kernel
>     and hence there is actually no need to pass it via DT. However, since
>     EFI stub follows EFI application calling conventions, it needs to
>     know the boot Hart ID so that it can pass it to the proper kernel via
>     a0. For this issue, the solution was to add "/chosen/boot-hartid" in
>     DT. Both EDK2 and u-boot append this node in DT.
> 
>     But above approach causes issue for ACPI since ACPI initialization
>     happens late in the proper kernel. Same is true even if we pass this
>     information via SMBIOS.
> 
>     Do you have any suggestions what can be done in ACPI case? Can we use
>     a UEFI variable with RVI specific GUID to pass this information? This
>     will have the advantage that it can work with either DT or ACPI.
>     Also, we may not need any UEFI spec update. Do you see any issue with
>     this approach? Your inputs will be very helpful.

What happened to your suggestions in

https://linuxplumbersconf.org/event/11/contributions/1099/attachments/781/1602/LPC_2021_ACPI_RISCV_Sunil.pdf

Best regards

Heinrich

> 
> Thanks!
> Sunil
> 


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Re: Question regarding "boot-hartid" DT node

[Sunil V L]

Hi Heinrich,
On Thu, Dec 02, 2021 at 04:09:34PM +0100, Heinrich Schuchardt wrote:
> On 12/2/21 16:05, Sunil V L wrote:
> > Hi All,
> >     I am starting this thread to discuss about the "boot-hartid" DT node
> >     that is being used in RISC-V Linux EFI stub.
> > 
> >     As you know, the boot Hart ID is passed in a0 register to the kernel
> >     and hence there is actually no need to pass it via DT. However, since
> >     EFI stub follows EFI application calling conventions, it needs to
> >     know the boot Hart ID so that it can pass it to the proper kernel via
> >     a0. For this issue, the solution was to add "/chosen/boot-hartid" in
> >     DT. Both EDK2 and u-boot append this node in DT.
> > 
> >     But above approach causes issue for ACPI since ACPI initialization
> >     happens late in the proper kernel. Same is true even if we pass this
> >     information via SMBIOS.
> > 
> >     Do you have any suggestions what can be done in ACPI case? Can we use
> >     a UEFI variable with RVI specific GUID to pass this information? This
> >     will have the advantage that it can work with either DT or ACPI.
> >     Also, we may not need any UEFI spec update. Do you see any issue with
> >     this approach? Your inputs will be very helpful.
> 
> What happened to your suggestions in
> 
> https://linuxplumbersconf.org/event/11/contributions/1099/attachments/781/1602/LPC_2021_ACPI_RISCV_Sunil.pdf

The challenge is, the EFI stub part which comes very early even before
proper kernel starts. If the information required in later stage of the
kernel, we can use ACPI tables. 

Thanks
Sunil

> 
> Best regards
> 
> Heinrich
> 
> > 
> > Thanks!
> > Sunil
> > 
> 

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Re: Question regarding "boot-hartid" DT node

[Heinrich Schuchardt]

On 12/2/21 16:17, Sunil V L wrote:
> Hi Heinrich,
> On Thu, Dec 02, 2021 at 04:09:34PM +0100, Heinrich Schuchardt wrote:
>> On 12/2/21 16:05, Sunil V L wrote:
>>> Hi All,
>>>      I am starting this thread to discuss about the "boot-hartid" DT node
>>>      that is being used in RISC-V Linux EFI stub.
>>>
>>>      As you know, the boot Hart ID is passed in a0 register to the kernel
>>>      and hence there is actually no need to pass it via DT. However, since
>>>      EFI stub follows EFI application calling conventions, it needs to
>>>      know the boot Hart ID so that it can pass it to the proper kernel via
>>>      a0. For this issue, the solution was to add "/chosen/boot-hartid" in
>>>      DT. Both EDK2 and u-boot append this node in DT.
>>>
>>>      But above approach causes issue for ACPI since ACPI initialization
>>>      happens late in the proper kernel. Same is true even if we pass this
>>>      information via SMBIOS.
>>>
>>>      Do you have any suggestions what can be done in ACPI case? Can we use
>>>      a UEFI variable with RVI specific GUID to pass this information? This
>>>      will have the advantage that it can work with either DT or ACPI.
>>>      Also, we may not need any UEFI spec update. Do you see any issue with
>>>      this approach? Your inputs will be very helpful.
>>
>> What happened to your suggestions in
>>
>> https://linuxplumbersconf.org/event/11/contributions/1099/attachments/781/1602/LPC_2021_ACPI_RISCV_Sunil.pdf
> 
> The challenge is, the EFI stub part which comes very early even before
> proper kernel starts. If the information required in later stage of the
> kernel, we can use ACPI tables.

What I have never understood is why the core calling the EFI stub cannot 
identify it own hartid which is stored in CSR mhartid. The missing piece 
seems to be SBI support to read this piece of information. That way we 
could get rid of passing the boot hartid via a0.

Best regards

Heinrich

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Re: Question regarding "boot-hartid" DT node

[Ard Biesheuvel]

On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com> wrote:
>
> Hi All,
>    I am starting this thread to discuss about the "boot-hartid" DT node
>    that is being used in RISC-V Linux EFI stub.
>
>    As you know, the boot Hart ID is passed in a0 register to the kernel
>    and hence there is actually no need to pass it via DT. However, since
>    EFI stub follows EFI application calling conventions, it needs to
>    know the boot Hart ID so that it can pass it to the proper kernel via
>    a0. For this issue, the solution was to add "/chosen/boot-hartid" in
>    DT. Both EDK2 and u-boot append this node in DT.
>

I think this was a mistake tbh

>    But above approach causes issue for ACPI since ACPI initialization
>    happens late in the proper kernel. Same is true even if we pass this
>    information via SMBIOS.
>

It would be better to define a RISCV specific EFI protocol that the
stub can call to discover the boot-hartid value. That wat, it can pass
it directly, without having to rely on firmware tables.

Note that you don't need any spec changes for this on the ACPI or UEFI side.

>    Do you have any suggestions what can be done in ACPI case? Can we use
>    a UEFI variable with RVI specific GUID to pass this information? This
>    will have the advantage that it can work with either DT or ACPI.
>    Also, we may not need any UEFI spec update. Do you see any issue with
>    this approach? Your inputs will be very helpful.
>
> Thanks!
> Sunil

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Re: Question regarding "boot-hartid" DT node

[Heinrich Schuchardt]

On 12/2/21 17:20, Ard Biesheuvel wrote:
> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com> wrote:
>>
>> Hi All,
>>     I am starting this thread to discuss about the "boot-hartid" DT node
>>     that is being used in RISC-V Linux EFI stub.
>>
>>     As you know, the boot Hart ID is passed in a0 register to the kernel
>>     and hence there is actually no need to pass it via DT. However, since
>>     EFI stub follows EFI application calling conventions, it needs to
>>     know the boot Hart ID so that it can pass it to the proper kernel via
>>     a0. For this issue, the solution was to add "/chosen/boot-hartid" in
>>     DT. Both EDK2 and u-boot append this node in DT.
>>
> 
> I think this was a mistake tbh
> 
>>     But above approach causes issue for ACPI since ACPI initialization
>>     happens late in the proper kernel. Same is true even if we pass this
>>     information via SMBIOS.
>>
> 
> It would be better to define a RISCV specific EFI protocol that the
> stub can call to discover the boot-hartid value. That wat, it can pass
> it directly, without having to rely on firmware tables.

As discovering the current process' hartid is not a UEFI specific task 
SBI would be a better fit.

Best regards

Heinrich

> 
> Note that you don't need any spec changes for this on the ACPI or UEFI side.
> 
>>     Do you have any suggestions what can be done in ACPI case? Can we use
>>     a UEFI variable with RVI specific GUID to pass this information? This
>>     will have the advantage that it can work with either DT or ACPI.
>>     Also, we may not need any UEFI spec update. Do you see any issue with
>>     this approach? Your inputs will be very helpful.
>>
>> Thanks!
>> Sunil


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Re: Question regarding "boot-hartid" DT node

[Ard Biesheuvel]

On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
<heinrich.schuchardt@canonical.com> wrote:
>
> On 12/2/21 17:20, Ard Biesheuvel wrote:
> > On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com> wrote:
> >>
> >> Hi All,
> >>     I am starting this thread to discuss about the "boot-hartid" DT node
> >>     that is being used in RISC-V Linux EFI stub.
> >>
> >>     As you know, the boot Hart ID is passed in a0 register to the kernel
> >>     and hence there is actually no need to pass it via DT. However, since
> >>     EFI stub follows EFI application calling conventions, it needs to
> >>     know the boot Hart ID so that it can pass it to the proper kernel via
> >>     a0. For this issue, the solution was to add "/chosen/boot-hartid" in
> >>     DT. Both EDK2 and u-boot append this node in DT.
> >>
> >
> > I think this was a mistake tbh
> >
> >>     But above approach causes issue for ACPI since ACPI initialization
> >>     happens late in the proper kernel. Same is true even if we pass this
> >>     information via SMBIOS.
> >>
> >
> > It would be better to define a RISCV specific EFI protocol that the
> > stub can call to discover the boot-hartid value. That wat, it can pass
> > it directly, without having to rely on firmware tables.
>
> As discovering the current process' hartid is not a UEFI specific task
> SBI would be a better fit.
>

I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
the EFI stub needs to ask the firmware which boot-hartid it should
pass in A0, it should use a EFI protocol and nothing else.

Whether or not the loader/firmware *implements* this EFI protocol by
calling into SBI is a different matter (and likely the best choice).
But that does not mean the EFI stub should make SBI calls directly.

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Re: Question regarding "boot-hartid" DT node

[Heinrich Schuchardt]

On 12/2/21 17:58, Ard Biesheuvel wrote:
> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> <heinrich.schuchardt@canonical.com> wrote:
>>
>> On 12/2/21 17:20, Ard Biesheuvel wrote:
>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com> wrote:
>>>>
>>>> Hi All,
>>>>      I am starting this thread to discuss about the "boot-hartid" DT node
>>>>      that is being used in RISC-V Linux EFI stub.
>>>>
>>>>      As you know, the boot Hart ID is passed in a0 register to the kernel
>>>>      and hence there is actually no need to pass it via DT. However, since
>>>>      EFI stub follows EFI application calling conventions, it needs to
>>>>      know the boot Hart ID so that it can pass it to the proper kernel via
>>>>      a0. For this issue, the solution was to add "/chosen/boot-hartid" in
>>>>      DT. Both EDK2 and u-boot append this node in DT.
>>>>
>>>
>>> I think this was a mistake tbh
>>>
>>>>      But above approach causes issue for ACPI since ACPI initialization
>>>>      happens late in the proper kernel. Same is true even if we pass this
>>>>      information via SMBIOS.
>>>>
>>>
>>> It would be better to define a RISCV specific EFI protocol that the
>>> stub can call to discover the boot-hartid value. That wat, it can pass
>>> it directly, without having to rely on firmware tables.
>>
>> As discovering the current process' hartid is not a UEFI specific task
>> SBI would be a better fit.
>>
> 
> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> the EFI stub needs to ask the firmware which boot-hartid it should
> pass in A0, it should use a EFI protocol and nothing else.
> 
> Whether or not the loader/firmware *implements* this EFI protocol by
> calling into SBI is a different matter (and likely the best choice).
> But that does not mean the EFI stub should make SBI calls directly.
>

The EFI stub does not need the boot-hartid. It is the main Linux kernel 
that does. And that kernel already implements SBI calls.

The main kernel could just try to read CSR mhartid which fails in S-mode 
and the SBI could emulate it.

Best regards

Heinrich

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Re: Question regarding "boot-hartid" DT node

[Ard Biesheuvel]

On Thu, 2 Dec 2021 at 18:04, Heinrich Schuchardt
<heinrich.schuchardt@canonical.com> wrote:
>
> On 12/2/21 17:58, Ard Biesheuvel wrote:
> > On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> > <heinrich.schuchardt@canonical.com> wrote:
> >>
> >> On 12/2/21 17:20, Ard Biesheuvel wrote:
> >>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com> wrote:
> >>>>
> >>>> Hi All,
> >>>>      I am starting this thread to discuss about the "boot-hartid" DT node
> >>>>      that is being used in RISC-V Linux EFI stub.
> >>>>
> >>>>      As you know, the boot Hart ID is passed in a0 register to the kernel
> >>>>      and hence there is actually no need to pass it via DT. However, since
> >>>>      EFI stub follows EFI application calling conventions, it needs to
> >>>>      know the boot Hart ID so that it can pass it to the proper kernel via
> >>>>      a0. For this issue, the solution was to add "/chosen/boot-hartid" in
> >>>>      DT. Both EDK2 and u-boot append this node in DT.
> >>>>
> >>>
> >>> I think this was a mistake tbh
> >>>
> >>>>      But above approach causes issue for ACPI since ACPI initialization
> >>>>      happens late in the proper kernel. Same is true even if we pass this
> >>>>      information via SMBIOS.
> >>>>
> >>>
> >>> It would be better to define a RISCV specific EFI protocol that the
> >>> stub can call to discover the boot-hartid value. That wat, it can pass
> >>> it directly, without having to rely on firmware tables.
> >>
> >> As discovering the current process' hartid is not a UEFI specific task
> >> SBI would be a better fit.
> >>
> >
> > I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> > the EFI stub needs to ask the firmware which boot-hartid it should
> > pass in A0, it should use a EFI protocol and nothing else.
> >
> > Whether or not the loader/firmware *implements* this EFI protocol by
> > calling into SBI is a different matter (and likely the best choice).
> > But that does not mean the EFI stub should make SBI calls directly.
> >
>
> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> that does. And that kernel already implements SBI calls.
>
> The main kernel could just try to read CSR mhartid which fails in S-mode
> and the SBI could emulate it.
>

That works for me as well, as long as the EFI stub does not have to
grow support for protocols beyond EFI based ones.

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Re: Question regarding "boot-hartid" DT node

[Atish Patra]

On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
<heinrich.schuchardt@canonical.com> wrote:
>
> On 12/2/21 17:58, Ard Biesheuvel wrote:
> > On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> > <heinrich.schuchardt@canonical.com> wrote:
> >>
> >> On 12/2/21 17:20, Ard Biesheuvel wrote:
> >>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com> wrote:
> >>>>
> >>>> Hi All,
> >>>>      I am starting this thread to discuss about the "boot-hartid" DT node
> >>>>      that is being used in RISC-V Linux EFI stub.
> >>>>
> >>>>      As you know, the boot Hart ID is passed in a0 register to the kernel
> >>>>      and hence there is actually no need to pass it via DT. However, since
> >>>>      EFI stub follows EFI application calling conventions, it needs to
> >>>>      know the boot Hart ID so that it can pass it to the proper kernel via
> >>>>      a0. For this issue, the solution was to add "/chosen/boot-hartid" in
> >>>>      DT. Both EDK2 and u-boot append this node in DT.
> >>>>
> >>>
> >>> I think this was a mistake tbh
> >>>
> >>>>      But above approach causes issue for ACPI since ACPI initialization
> >>>>      happens late in the proper kernel. Same is true even if we pass this
> >>>>      information via SMBIOS.
> >>>>
> >>>
> >>> It would be better to define a RISCV specific EFI protocol that the
> >>> stub can call to discover the boot-hartid value. That wat, it can pass
> >>> it directly, without having to rely on firmware tables.
> >>
> >> As discovering the current process' hartid is not a UEFI specific task
> >> SBI would be a better fit.
> >>
> >
> > I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> > the EFI stub needs to ask the firmware which boot-hartid it should
> > pass in A0, it should use a EFI protocol and nothing else.
> >
> > Whether or not the loader/firmware *implements* this EFI protocol by
> > calling into SBI is a different matter (and likely the best choice).
> > But that does not mean the EFI stub should make SBI calls directly.
> >
>
> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> that does. And that kernel already implements SBI calls.
>
> The main kernel could just try to read CSR mhartid which fails in S-mode
> and the SBI could emulate it.

New SBI extension should be added only if there is no other way to
solve a generic
problem. The boot hartid issue is very specific to efi booting only.
Any system that doesn't require
EFI booting won't need it. Even for EFI booting, we have other
approaches already proposed
to solve it. That's why, SBI extension should be the last resort
rather than first.

I think an RISC-V specific EFI protocol as suggested by Ard should
work for all the cases.
Is there a case where you think it may not work ? U-Boot & EDK2
already stores the boot hartid.
They just implement that protocol and pass the hartid to the caller.
We do need to support it in the grub though.

@Heinrich Schuchardt
I vaguely remember you proposed something similar when we discussed
this first during FOSDEM.
I can't recall why it was abandoned in favor of the DT approach which
works. But,
it is not an ideal solution considering RISC-V ACPI support is already
on the way.

Do you have a link to the older thread where this thing was discussed ?


>
> Best regards
>
> Heinrich
>
> _______________________________________________
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--
Regards,
Atish

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Re: Question regarding "boot-hartid" DT node

[Ard Biesheuvel]

On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
>
> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> <heinrich.schuchardt@canonical.com> wrote:
> >
> > On 12/2/21 17:58, Ard Biesheuvel wrote:
> > > On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> > > <heinrich.schuchardt@canonical.com> wrote:
> > >>
> > >> On 12/2/21 17:20, Ard Biesheuvel wrote:
> > >>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com> wrote:
> > >>>>
> > >>>> Hi All,
> > >>>>      I am starting this thread to discuss about the "boot-hartid" DT node
> > >>>>      that is being used in RISC-V Linux EFI stub.
> > >>>>
> > >>>>      As you know, the boot Hart ID is passed in a0 register to the kernel
> > >>>>      and hence there is actually no need to pass it via DT. However, since
> > >>>>      EFI stub follows EFI application calling conventions, it needs to
> > >>>>      know the boot Hart ID so that it can pass it to the proper kernel via
> > >>>>      a0. For this issue, the solution was to add "/chosen/boot-hartid" in
> > >>>>      DT. Both EDK2 and u-boot append this node in DT.
> > >>>>
> > >>>
> > >>> I think this was a mistake tbh
> > >>>
> > >>>>      But above approach causes issue for ACPI since ACPI initialization
> > >>>>      happens late in the proper kernel. Same is true even if we pass this
> > >>>>      information via SMBIOS.
> > >>>>
> > >>>
> > >>> It would be better to define a RISCV specific EFI protocol that the
> > >>> stub can call to discover the boot-hartid value. That wat, it can pass
> > >>> it directly, without having to rely on firmware tables.
> > >>
> > >> As discovering the current process' hartid is not a UEFI specific task
> > >> SBI would be a better fit.
> > >>
> > >
> > > I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> > > the EFI stub needs to ask the firmware which boot-hartid it should
> > > pass in A0, it should use a EFI protocol and nothing else.
> > >
> > > Whether or not the loader/firmware *implements* this EFI protocol by
> > > calling into SBI is a different matter (and likely the best choice).
> > > But that does not mean the EFI stub should make SBI calls directly.
> > >
> >
> > The EFI stub does not need the boot-hartid. It is the main Linux kernel
> > that does. And that kernel already implements SBI calls.
> >
> > The main kernel could just try to read CSR mhartid which fails in S-mode
> > and the SBI could emulate it.
>
> New SBI extension should be added only if there is no other way to
> solve a generic
> problem. The boot hartid issue is very specific to efi booting only.
> Any system that doesn't require
> EFI booting won't need it. Even for EFI booting, we have other
> approaches already proposed
> to solve it. That's why, SBI extension should be the last resort
> rather than first.
>
> I think an RISC-V specific EFI protocol as suggested by Ard should
> work for all the cases.
> Is there a case where you think it may not work ? U-Boot & EDK2
> already stores the boot hartid.
> They just implement that protocol and pass the hartid to the caller.
> We do need to support it in the grub though.
>

Why would GRUB care about this? The EFI stub will call into the
underlying firmware to invoke the protocol, GRUB is just a loader with
a fancy menu that allows you to select which image to load, no?

> @Heinrich Schuchardt
> I vaguely remember you proposed something similar when we discussed
> this first during FOSDEM.
> I can't recall why it was abandoned in favor of the DT approach which
> works. But,
> it is not an ideal solution considering RISC-V ACPI support is already
> on the way.
>
> Do you have a link to the older thread where this thing was discussed ?
>
>
> >
> > Best regards
> >
> > Heinrich
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>
>
>
> --
> Regards,
> Atish

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Re: Question regarding "boot-hartid" DT node

[Heinrich Schuchardt]

On 12/3/21 11:13, Ard Biesheuvel wrote:
> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
>>
>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
>> <heinrich.schuchardt@canonical.com> wrote:
>>>
>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>
>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com> wrote:
>>>>>>>
>>>>>>> Hi All,
>>>>>>>       I am starting this thread to discuss about the "boot-hartid" DT node
>>>>>>>       that is being used in RISC-V Linux EFI stub.
>>>>>>>
>>>>>>>       As you know, the boot Hart ID is passed in a0 register to the kernel
>>>>>>>       and hence there is actually no need to pass it via DT. However, since
>>>>>>>       EFI stub follows EFI application calling conventions, it needs to
>>>>>>>       know the boot Hart ID so that it can pass it to the proper kernel via
>>>>>>>       a0. For this issue, the solution was to add "/chosen/boot-hartid" in
>>>>>>>       DT. Both EDK2 and u-boot append this node in DT.
>>>>>>>
>>>>>>
>>>>>> I think this was a mistake tbh
>>>>>>
>>>>>>>       But above approach causes issue for ACPI since ACPI initialization
>>>>>>>       happens late in the proper kernel. Same is true even if we pass this
>>>>>>>       information via SMBIOS.
>>>>>>>
>>>>>>
>>>>>> It would be better to define a RISCV specific EFI protocol that the
>>>>>> stub can call to discover the boot-hartid value. That wat, it can pass
>>>>>> it directly, without having to rely on firmware tables.
>>>>>
>>>>> As discovering the current process' hartid is not a UEFI specific task
>>>>> SBI would be a better fit.
>>>>>
>>>>
>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
>>>> the EFI stub needs to ask the firmware which boot-hartid it should
>>>> pass in A0, it should use a EFI protocol and nothing else.
>>>>
>>>> Whether or not the loader/firmware *implements* this EFI protocol by
>>>> calling into SBI is a different matter (and likely the best choice).
>>>> But that does not mean the EFI stub should make SBI calls directly.
>>>>
>>>
>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
>>> that does. And that kernel already implements SBI calls.
>>>
>>> The main kernel could just try to read CSR mhartid which fails in S-mode
>>> and the SBI could emulate it.
>>
>> New SBI extension should be added only if there is no other way to
>> solve a generic

I am not sure this feature would be implemented as SBI extension or as a 
CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require 
an update of the SBI specification.

>> problem. The boot hartid issue is very specific to efi booting only.
>> Any system that doesn't require

The boot hartid is not EFI related at all. A firmware running single 
threaded does not need this information.

Information about the boot hartid is a general OS need.

I am wondering why S-mode software should not have a generic means to 
find out on which hart it is currently running.

>> EFI booting won't need it. Even for EFI booting, we have other
>> approaches already proposed
>> to solve it. That's why, SBI extension should be the last resort
>> rather than first.
>>
>> I think an RISC-V specific EFI protocol as suggested by Ard should
>> work for all the cases.
>> Is there a case where you think it may not work ? U-Boot & EDK2
>> already stores the boot hartid.
>> They just implement that protocol and pass the hartid to the caller.
>> We do need to support it in the grub though.
>>
> 
> Why would GRUB care about this? The EFI stub will call into the
> underlying firmware to invoke the protocol, GRUB is just a loader with
> a fancy menu that allows you to select which image to load, no?

This is a related discussion:

https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029

If GRUB loads a devicetree it will anyway have to call into the firmware 
for fixups. These will include adding the boot-hartid.

> 
>> @Heinrich Schuchardt
>> I vaguely remember you proposed something similar when we discussed
>> this first during FOSDEM.
>> I can't recall why it was abandoned in favor of the DT approach which
>> works. But,
>> it is not an ideal solution considering RISC-V ACPI support is already
>> on the way.
>>
>> Do you have a link to the older thread where this thing was discussed ?

Unfortunately I cannot find anything.

Best regards

Heinrich

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Re: Question regarding "boot-hartid" DT node

[Heinrich Schuchardt]

On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> On 12/3/21 11:13, Ard Biesheuvel wrote:
>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
>>>
>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>
>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
>>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>>
>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
>>>>>>> wrote:
>>>>>>>>
>>>>>>>> Hi All,
>>>>>>>>       I am starting this thread to discuss about the
>>>>>>>> "boot-hartid" DT node
>>>>>>>>       that is being used in RISC-V Linux EFI stub.
>>>>>>>>
>>>>>>>>       As you know, the boot Hart ID is passed in a0 register to
>>>>>>>> the kernel
>>>>>>>>       and hence there is actually no need to pass it via DT.
>>>>>>>> However, since
>>>>>>>>       EFI stub follows EFI application calling conventions, it
>>>>>>>> needs to
>>>>>>>>       know the boot Hart ID so that it can pass it to the proper
>>>>>>>> kernel via
>>>>>>>>       a0. For this issue, the solution was to add
>>>>>>>> "/chosen/boot-hartid" in
>>>>>>>>       DT. Both EDK2 and u-boot append this node in DT.
>>>>>>>>
>>>>>>>
>>>>>>> I think this was a mistake tbh
>>>>>>>
>>>>>>>>       But above approach causes issue for ACPI since ACPI
>>>>>>>> initialization
>>>>>>>>       happens late in the proper kernel. Same is true even if we
>>>>>>>> pass this
>>>>>>>>       information via SMBIOS.
>>>>>>>>
>>>>>>>
>>>>>>> It would be better to define a RISCV specific EFI protocol that the
>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
>>>>>>> pass
>>>>>>> it directly, without having to rely on firmware tables.
>>>>>>
>>>>>> As discovering the current process' hartid is not a UEFI specific
>>>>>> task
>>>>>> SBI would be a better fit.
>>>>>>
>>>>>
>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
>>>>> pass in A0, it should use a EFI protocol and nothing else.
>>>>>
>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
>>>>> calling into SBI is a different matter (and likely the best choice).
>>>>> But that does not mean the EFI stub should make SBI calls directly.
>>>>>
>>>>
>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
>>>> that does. And that kernel already implements SBI calls.
>>>>
>>>> The main kernel could just try to read CSR mhartid which fails in
>>>> S-mode
>>>> and the SBI could emulate it.
>>>
>>> New SBI extension should be added only if there is no other way to
>>> solve a generic
>
> I am not sure this feature would be implemented as SBI extension or as a
> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
> an update of the SBI specification.
>
>>> problem. The boot hartid issue is very specific to efi booting only.
>>> Any system that doesn't require
>
> The boot hartid is not EFI related at all. A firmware running single
> threaded does not need this information.
>
> Information about the boot hartid is a general OS need.
>
> I am wondering why S-mode software should not have a generic means to
> find out on which hart it is currently running.
>
>>> EFI booting won't need it. Even for EFI booting, we have other
>>> approaches already proposed
>>> to solve it. That's why, SBI extension should be the last resort
>>> rather than first.
>>>
>>> I think an RISC-V specific EFI protocol as suggested by Ard should
>>> work for all the cases.
>>> Is there a case where you think it may not work ? U-Boot & EDK2
>>> already stores the boot hartid.
>>> They just implement that protocol and pass the hartid to the caller.
>>> We do need to support it in the grub though.
>>>
>>
>> Why would GRUB care about this? The EFI stub will call into the
>> underlying firmware to invoke the protocol, GRUB is just a loader with
>> a fancy menu that allows you to select which image to load, no?
>
> This is a related discussion:
>
> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
>
>
> If GRUB loads a devicetree it will anyway have to call into the firmware
> for fixups. These will include adding the boot-hartid.
>
>>
>>> @Heinrich Schuchardt
>>> I vaguely remember you proposed something similar when we discussed
>>> this first during FOSDEM.
>>> I can't recall why it was abandoned in favor of the DT approach which
>>> works. But,
>>> it is not an ideal solution considering RISC-V ACPI support is already
>>> on the way.
>>>
>>> Do you have a link to the older thread where this thing was discussed ?
>
> Unfortunately I cannot find anything.

I assume Atish referred to this thread:

https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/

Best regards

Heinrich

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Re: Question regarding "boot-hartid" DT node

[Atish Patra]

On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
>
> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> > On 12/3/21 11:13, Ard Biesheuvel wrote:
> >> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
> >>>
> >>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> >>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>
> >>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
> >>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> >>>>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>>>
> >>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
> >>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
> >>>>>>> wrote:
> >>>>>>>>
> >>>>>>>> Hi All,
> >>>>>>>>       I am starting this thread to discuss about the
> >>>>>>>> "boot-hartid" DT node
> >>>>>>>>       that is being used in RISC-V Linux EFI stub.
> >>>>>>>>
> >>>>>>>>       As you know, the boot Hart ID is passed in a0 register to
> >>>>>>>> the kernel
> >>>>>>>>       and hence there is actually no need to pass it via DT.
> >>>>>>>> However, since
> >>>>>>>>       EFI stub follows EFI application calling conventions, it
> >>>>>>>> needs to
> >>>>>>>>       know the boot Hart ID so that it can pass it to the proper
> >>>>>>>> kernel via
> >>>>>>>>       a0. For this issue, the solution was to add
> >>>>>>>> "/chosen/boot-hartid" in
> >>>>>>>>       DT. Both EDK2 and u-boot append this node in DT.
> >>>>>>>>
> >>>>>>>
> >>>>>>> I think this was a mistake tbh
> >>>>>>>
> >>>>>>>>       But above approach causes issue for ACPI since ACPI
> >>>>>>>> initialization
> >>>>>>>>       happens late in the proper kernel. Same is true even if we
> >>>>>>>> pass this
> >>>>>>>>       information via SMBIOS.
> >>>>>>>>
> >>>>>>>
> >>>>>>> It would be better to define a RISCV specific EFI protocol that the
> >>>>>>> stub can call to discover the boot-hartid value. That wat, it can
> >>>>>>> pass
> >>>>>>> it directly, without having to rely on firmware tables.
> >>>>>>
> >>>>>> As discovering the current process' hartid is not a UEFI specific
> >>>>>> task
> >>>>>> SBI would be a better fit.
> >>>>>>
> >>>>>
> >>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> >>>>> the EFI stub needs to ask the firmware which boot-hartid it should
> >>>>> pass in A0, it should use a EFI protocol and nothing else.
> >>>>>
> >>>>> Whether or not the loader/firmware *implements* this EFI protocol by
> >>>>> calling into SBI is a different matter (and likely the best choice).
> >>>>> But that does not mean the EFI stub should make SBI calls directly.
> >>>>>
> >>>>
> >>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> >>>> that does. And that kernel already implements SBI calls.
> >>>>
> >>>> The main kernel could just try to read CSR mhartid which fails in
> >>>> S-mode
> >>>> and the SBI could emulate it.
> >>>
> >>> New SBI extension should be added only if there is no other way to
> >>> solve a generic
> >
> > I am not sure this feature would be implemented as SBI extension or as a
> > CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
> > an update of the SBI specification.
> >
> >>> problem. The boot hartid issue is very specific to efi booting only.
> >>> Any system that doesn't require
> >
> > The boot hartid is not EFI related at all. A firmware running single
> > threaded does not need this information.
> >
> > Information about the boot hartid is a general OS need.
> >
> > I am wondering why S-mode software should not have a generic means to
> > find out on which hart it is currently running.
> >
> >>> EFI booting won't need it. Even for EFI booting, we have other
> >>> approaches already proposed
> >>> to solve it. That's why, SBI extension should be the last resort
> >>> rather than first.
> >>>
> >>> I think an RISC-V specific EFI protocol as suggested by Ard should
> >>> work for all the cases.
> >>> Is there a case where you think it may not work ? U-Boot & EDK2
> >>> already stores the boot hartid.
> >>> They just implement that protocol and pass the hartid to the caller.
> >>> We do need to support it in the grub though.
> >>>
> >>
> >> Why would GRUB care about this? The EFI stub will call into the
> >> underlying firmware to invoke the protocol, GRUB is just a loader with
> >> a fancy menu that allows you to select which image to load, no?
> >
> > This is a related discussion:
> >
> > https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
> >

Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
still debating the same topic :).
Let me summarize the thread. There are multiple ways for EFI stub code
to retrieve the boot hartid.

1. EFI variables - This is what Henerich proposed last time. Ard
suggested that EFI configuration tables are better candidates than EFI
variables.
2. DT modification - This was preferred over the configuration table
at that time given because RISC-V was DT only at that time.
                                 We already had all the infrastructure
around DT. Thus, DT seemed to be a natural choice then.
                                 It works now for existing setup
however, the DT approach will not work for systems with ACPI support.
                                 Adding a similar entry in ACPI tables
is possible but adding ACPI support in EFI stub is not trivial.
3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
mandatory and adding SMBIOS support in EFI stub is not trivial.
4. SBI         -  As I mentioned before, this is an EFI specific
problem because EFI stub doesn't know what the boot hartid is. Thus,
it should be solved
                      in an EFI specific way. An SBI extension for
such features may not be acceptable as the non-EFI booting method
works fine without the SBI extension.
5. RISC-V specific EFI configuration table or protocol: Ard suggested
EFI configuration table last time. Earlier in this thread, EFI
protocol was suggested.
                      My personal preference has always been one of
these as it solves the problem for all EFI booting methods
                      for platforms-os
combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.

@Heinrich: Do you see any issue with the EFI configuration table or
protocol to retrieve the boot hartid?

My only concern with the RISC-V EFI protocol is that Ard suggested it
doesn't need a modification in UEFI spec.
Where should we document it in this case ? We can't document it in
Linux or EBBR.
Because, this is a protocol that server systems and other non-Linux OS
will also use.
We can define it in the RISC-V platform spec. But that's not the usual
place where somebody will look for the definition of such protocol.

Wouldn't it be better to standardize it in UEFI spec ? The UEFI spec
already has ARCH specific protocols/config tables.

> >
> > If GRUB loads a devicetree it will anyway have to call into the firmware
> > for fixups. These will include adding the boot-hartid.
> >
> >>
> >>> @Heinrich Schuchardt
> >>> I vaguely remember you proposed something similar when we discussed
> >>> this first during FOSDEM.
> >>> I can't recall why it was abandoned in favor of the DT approach which
> >>> works. But,
> >>> it is not an ideal solution considering RISC-V ACPI support is already
> >>> on the way.
> >>>
> >>> Do you have a link to the older thread where this thing was discussed ?
> >
> > Unfortunately I cannot find anything.
>
> I assume Atish referred to this thread:
>
> https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/
>
> Best regards
>
> Heinrich
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv



-- 
Regards,
Atish

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Re: Question regarding "boot-hartid" DT node

[Heinrich Schuchardt]

On 12/4/21 01:44, Atish Patra wrote:
> On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
>>
>> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
>>> On 12/3/21 11:13, Ard Biesheuvel wrote:
>>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
>>>>>
>>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
>>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>>
>>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
>>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>>>>
>>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
>>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>> Hi All,
>>>>>>>>>>        I am starting this thread to discuss about the
>>>>>>>>>> "boot-hartid" DT node
>>>>>>>>>>        that is being used in RISC-V Linux EFI stub.
>>>>>>>>>>
>>>>>>>>>>        As you know, the boot Hart ID is passed in a0 register to
>>>>>>>>>> the kernel
>>>>>>>>>>        and hence there is actually no need to pass it via DT.
>>>>>>>>>> However, since
>>>>>>>>>>        EFI stub follows EFI application calling conventions, it
>>>>>>>>>> needs to
>>>>>>>>>>        know the boot Hart ID so that it can pass it to the proper
>>>>>>>>>> kernel via
>>>>>>>>>>        a0. For this issue, the solution was to add
>>>>>>>>>> "/chosen/boot-hartid" in
>>>>>>>>>>        DT. Both EDK2 and u-boot append this node in DT.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I think this was a mistake tbh
>>>>>>>>>
>>>>>>>>>>        But above approach causes issue for ACPI since ACPI
>>>>>>>>>> initialization
>>>>>>>>>>        happens late in the proper kernel. Same is true even if we
>>>>>>>>>> pass this
>>>>>>>>>>        information via SMBIOS.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
>>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
>>>>>>>>> pass
>>>>>>>>> it directly, without having to rely on firmware tables.
>>>>>>>>
>>>>>>>> As discovering the current process' hartid is not a UEFI specific
>>>>>>>> task
>>>>>>>> SBI would be a better fit.
>>>>>>>>
>>>>>>>
>>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
>>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
>>>>>>> pass in A0, it should use a EFI protocol and nothing else.
>>>>>>>
>>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
>>>>>>> calling into SBI is a different matter (and likely the best choice).
>>>>>>> But that does not mean the EFI stub should make SBI calls directly.
>>>>>>>
>>>>>>
>>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
>>>>>> that does. And that kernel already implements SBI calls.
>>>>>>
>>>>>> The main kernel could just try to read CSR mhartid which fails in
>>>>>> S-mode
>>>>>> and the SBI could emulate it.
>>>>>
>>>>> New SBI extension should be added only if there is no other way to
>>>>> solve a generic
>>>
>>> I am not sure this feature would be implemented as SBI extension or as a
>>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
>>> an update of the SBI specification.
>>>
>>>>> problem. The boot hartid issue is very specific to efi booting only.
>>>>> Any system that doesn't require
>>>
>>> The boot hartid is not EFI related at all. A firmware running single
>>> threaded does not need this information.
>>>
>>> Information about the boot hartid is a general OS need.
>>>
>>> I am wondering why S-mode software should not have a generic means to
>>> find out on which hart it is currently running.
>>>
>>>>> EFI booting won't need it. Even for EFI booting, we have other
>>>>> approaches already proposed
>>>>> to solve it. That's why, SBI extension should be the last resort
>>>>> rather than first.
>>>>>
>>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
>>>>> work for all the cases.
>>>>> Is there a case where you think it may not work ? U-Boot & EDK2
>>>>> already stores the boot hartid.
>>>>> They just implement that protocol and pass the hartid to the caller.
>>>>> We do need to support it in the grub though.
>>>>>
>>>>
>>>> Why would GRUB care about this? The EFI stub will call into the
>>>> underlying firmware to invoke the protocol, GRUB is just a loader with
>>>> a fancy menu that allows you to select which image to load, no?
>>>
>>> This is a related discussion:
>>>
>>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
>>>
> 
> Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
> still debating the same topic :).
> Let me summarize the thread. There are multiple ways for EFI stub code
> to retrieve the boot hartid.
> 
> 1. EFI variables - This is what Henerich proposed last time. Ard
> suggested that EFI configuration tables are better candidates than EFI
> variables.
> 2. DT modification - This was preferred over the configuration table
> at that time given because RISC-V was DT only at that time.
>                                   We already had all the infrastructure
> around DT. Thus, DT seemed to be a natural choice then.
>                                   It works now for existing setup
> however, the DT approach will not work for systems with ACPI support.
>                                   Adding a similar entry in ACPI tables
> is possible but adding ACPI support in EFI stub is not trivial.
> 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
> mandatory and adding SMBIOS support in EFI stub is not trivial.
> 4. SBI         -  As I mentioned before, this is an EFI specific
> problem because EFI stub doesn't know what the boot hartid is. Thus,
> it should be solved
>                        in an EFI specific way. An SBI extension for
> such features may not be acceptable as the non-EFI booting method
> works fine without the SBI extension.
> 5. RISC-V specific EFI configuration table or protocol: Ard suggested
> EFI configuration table last time. Earlier in this thread, EFI
> protocol was suggested.
>                        My personal preference has always been one of
> these as it solves the problem for all EFI booting methods
>                        for platforms-os
> combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
> 
> @Heinrich: Do you see any issue with the EFI configuration table or
> protocol to retrieve the boot hartid?

There is nothing technical stopping us from implementing either option.

We could simply reuse the EFI Device Tree Fixup Protocol 
(https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in 
U-Boot and already used by systemd-boot. Pass a devicetree (which may be 
empty) to the Fixup() method and it will add the /chosen node with the 
boot-hartid parameter.

The EFI stub anyway creates a new device-tree to pass the memory map to 
the kernel in the ACPI case (function update_fdt()). Calling the EFI 
Device Tree Fixup Protocol could be easily added.

Best regards

Heinrich

> 
> My only concern with the RISC-V EFI protocol is that Ard suggested it
> doesn't need a modification in UEFI spec.
> Where should we document it in this case ? We can't document it in
> Linux or EBBR.
> Because, this is a protocol that server systems and other non-Linux OS
> will also use.
> We can define it in the RISC-V platform spec. But that's not the usual
> place where somebody will look for the definition of such protocol.
> 
> Wouldn't it be better to standardize it in UEFI spec ? The UEFI spec
> already has ARCH specific protocols/config tables.
> 
>>>
>>> If GRUB loads a devicetree it will anyway have to call into the firmware
>>> for fixups. These will include adding the boot-hartid.
>>>
>>>>
>>>>> @Heinrich Schuchardt
>>>>> I vaguely remember you proposed something similar when we discussed
>>>>> this first during FOSDEM.
>>>>> I can't recall why it was abandoned in favor of the DT approach which
>>>>> works. But,
>>>>> it is not an ideal solution considering RISC-V ACPI support is already
>>>>> on the way.
>>>>>
>>>>> Do you have a link to the older thread where this thing was discussed ?
>>>
>>> Unfortunately I cannot find anything.
>>
>> I assume Atish referred to this thread:
>>
>> https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/
>>
>> Best regards
>>
>> Heinrich
>>
>> _______________________________________________
>> linux-riscv mailing list
>> linux-riscv@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-riscv
> 
> 
> 

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Re: Question regarding "boot-hartid" DT node

[Anup Patel]

On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
<heinrich.schuchardt@canonical.com> wrote:
>
>
>
> On 12/4/21 01:44, Atish Patra wrote:
> > On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> >>
> >> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> >>> On 12/3/21 11:13, Ard Biesheuvel wrote:
> >>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
> >>>>>
> >>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> >>>>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>>>
> >>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
> >>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> >>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>>>>>
> >>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
> >>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
> >>>>>>>>> wrote:
> >>>>>>>>>>
> >>>>>>>>>> Hi All,
> >>>>>>>>>>        I am starting this thread to discuss about the
> >>>>>>>>>> "boot-hartid" DT node
> >>>>>>>>>>        that is being used in RISC-V Linux EFI stub.
> >>>>>>>>>>
> >>>>>>>>>>        As you know, the boot Hart ID is passed in a0 register to
> >>>>>>>>>> the kernel
> >>>>>>>>>>        and hence there is actually no need to pass it via DT.
> >>>>>>>>>> However, since
> >>>>>>>>>>        EFI stub follows EFI application calling conventions, it
> >>>>>>>>>> needs to
> >>>>>>>>>>        know the boot Hart ID so that it can pass it to the proper
> >>>>>>>>>> kernel via
> >>>>>>>>>>        a0. For this issue, the solution was to add
> >>>>>>>>>> "/chosen/boot-hartid" in
> >>>>>>>>>>        DT. Both EDK2 and u-boot append this node in DT.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> I think this was a mistake tbh
> >>>>>>>>>
> >>>>>>>>>>        But above approach causes issue for ACPI since ACPI
> >>>>>>>>>> initialization
> >>>>>>>>>>        happens late in the proper kernel. Same is true even if we
> >>>>>>>>>> pass this
> >>>>>>>>>>        information via SMBIOS.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
> >>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
> >>>>>>>>> pass
> >>>>>>>>> it directly, without having to rely on firmware tables.
> >>>>>>>>
> >>>>>>>> As discovering the current process' hartid is not a UEFI specific
> >>>>>>>> task
> >>>>>>>> SBI would be a better fit.
> >>>>>>>>
> >>>>>>>
> >>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> >>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
> >>>>>>> pass in A0, it should use a EFI protocol and nothing else.
> >>>>>>>
> >>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
> >>>>>>> calling into SBI is a different matter (and likely the best choice).
> >>>>>>> But that does not mean the EFI stub should make SBI calls directly.
> >>>>>>>
> >>>>>>
> >>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> >>>>>> that does. And that kernel already implements SBI calls.
> >>>>>>
> >>>>>> The main kernel could just try to read CSR mhartid which fails in
> >>>>>> S-mode
> >>>>>> and the SBI could emulate it.
> >>>>>
> >>>>> New SBI extension should be added only if there is no other way to
> >>>>> solve a generic
> >>>
> >>> I am not sure this feature would be implemented as SBI extension or as a
> >>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
> >>> an update of the SBI specification.
> >>>
> >>>>> problem. The boot hartid issue is very specific to efi booting only.
> >>>>> Any system that doesn't require
> >>>
> >>> The boot hartid is not EFI related at all. A firmware running single
> >>> threaded does not need this information.
> >>>
> >>> Information about the boot hartid is a general OS need.
> >>>
> >>> I am wondering why S-mode software should not have a generic means to
> >>> find out on which hart it is currently running.
> >>>
> >>>>> EFI booting won't need it. Even for EFI booting, we have other
> >>>>> approaches already proposed
> >>>>> to solve it. That's why, SBI extension should be the last resort
> >>>>> rather than first.
> >>>>>
> >>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
> >>>>> work for all the cases.
> >>>>> Is there a case where you think it may not work ? U-Boot & EDK2
> >>>>> already stores the boot hartid.
> >>>>> They just implement that protocol and pass the hartid to the caller.
> >>>>> We do need to support it in the grub though.
> >>>>>
> >>>>
> >>>> Why would GRUB care about this? The EFI stub will call into the
> >>>> underlying firmware to invoke the protocol, GRUB is just a loader with
> >>>> a fancy menu that allows you to select which image to load, no?
> >>>
> >>> This is a related discussion:
> >>>
> >>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
> >>>
> >
> > Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
> > still debating the same topic :).
> > Let me summarize the thread. There are multiple ways for EFI stub code
> > to retrieve the boot hartid.
> >
> > 1. EFI variables - This is what Henerich proposed last time. Ard
> > suggested that EFI configuration tables are better candidates than EFI
> > variables.
> > 2. DT modification - This was preferred over the configuration table
> > at that time given because RISC-V was DT only at that time.
> >                                   We already had all the infrastructure
> > around DT. Thus, DT seemed to be a natural choice then.
> >                                   It works now for existing setup
> > however, the DT approach will not work for systems with ACPI support.
> >                                   Adding a similar entry in ACPI tables
> > is possible but adding ACPI support in EFI stub is not trivial.
> > 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
> > mandatory and adding SMBIOS support in EFI stub is not trivial.
> > 4. SBI         -  As I mentioned before, this is an EFI specific
> > problem because EFI stub doesn't know what the boot hartid is. Thus,
> > it should be solved
> >                        in an EFI specific way. An SBI extension for
> > such features may not be acceptable as the non-EFI booting method
> > works fine without the SBI extension.
> > 5. RISC-V specific EFI configuration table or protocol: Ard suggested
> > EFI configuration table last time. Earlier in this thread, EFI
> > protocol was suggested.
> >                        My personal preference has always been one of
> > these as it solves the problem for all EFI booting methods
> >                        for platforms-os
> > combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
> >
> > @Heinrich: Do you see any issue with the EFI configuration table or
> > protocol to retrieve the boot hartid?
>
> There is nothing technical stopping us from implementing either option.
>
> We could simply reuse the EFI Device Tree Fixup Protocol
> (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
> U-Boot and already used by systemd-boot. Pass a devicetree (which may be
> empty) to the Fixup() method and it will add the /chosen node with the
> boot-hartid parameter.
>
> The EFI stub anyway creates a new device-tree to pass the memory map to
> the kernel in the ACPI case (function update_fdt()). Calling the EFI
> Device Tree Fixup Protocol could be easily added.

Are you suggesting that DTB (skeletal or full-blown) will always be there when
booting the kernel as an EFI application ? If yes then we are
indirectly mandating
skeletal DTB for UEFI+ACPI system.

Regards,
Anup

>
> Best regards
>
> Heinrich
>
> >
> > My only concern with the RISC-V EFI protocol is that Ard suggested it
> > doesn't need a modification in UEFI spec.
> > Where should we document it in this case ? We can't document it in
> > Linux or EBBR.
> > Because, this is a protocol that server systems and other non-Linux OS
> > will also use.
> > We can define it in the RISC-V platform spec. But that's not the usual
> > place where somebody will look for the definition of such protocol.
> >
> > Wouldn't it be better to standardize it in UEFI spec ? The UEFI spec
> > already has ARCH specific protocols/config tables.
> >
> >>>
> >>> If GRUB loads a devicetree it will anyway have to call into the firmware
> >>> for fixups. These will include adding the boot-hartid.
> >>>
> >>>>
> >>>>> @Heinrich Schuchardt
> >>>>> I vaguely remember you proposed something similar when we discussed
> >>>>> this first during FOSDEM.
> >>>>> I can't recall why it was abandoned in favor of the DT approach which
> >>>>> works. But,
> >>>>> it is not an ideal solution considering RISC-V ACPI support is already
> >>>>> on the way.
> >>>>>
> >>>>> Do you have a link to the older thread where this thing was discussed ?
> >>>
> >>> Unfortunately I cannot find anything.
> >>
> >> I assume Atish referred to this thread:
> >>
> >> https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/
> >>
> >> Best regards
> >>
> >> Heinrich
> >>
> >> _______________________________________________
> >> linux-riscv mailing list
> >> linux-riscv@lists.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-riscv
> >
> >
> >

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Re: Question regarding "boot-hartid" DT node

[Heinrich Schuchardt]

On 12/4/21 05:24, Anup Patel wrote:
> On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
> <heinrich.schuchardt@canonical.com> wrote:
>>
>>
>>
>> On 12/4/21 01:44, Atish Patra wrote:
>>> On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
>>>>
>>>> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
>>>>> On 12/3/21 11:13, Ard Biesheuvel wrote:
>>>>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
>>>>>>>
>>>>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>>>>
>>>>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
>>>>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
>>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>>>>>>
>>>>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
>>>>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
>>>>>>>>>>> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> Hi All,
>>>>>>>>>>>>         I am starting this thread to discuss about the
>>>>>>>>>>>> "boot-hartid" DT node
>>>>>>>>>>>>         that is being used in RISC-V Linux EFI stub.
>>>>>>>>>>>>
>>>>>>>>>>>>         As you know, the boot Hart ID is passed in a0 register to
>>>>>>>>>>>> the kernel
>>>>>>>>>>>>         and hence there is actually no need to pass it via DT.
>>>>>>>>>>>> However, since
>>>>>>>>>>>>         EFI stub follows EFI application calling conventions, it
>>>>>>>>>>>> needs to
>>>>>>>>>>>>         know the boot Hart ID so that it can pass it to the proper
>>>>>>>>>>>> kernel via
>>>>>>>>>>>>         a0. For this issue, the solution was to add
>>>>>>>>>>>> "/chosen/boot-hartid" in
>>>>>>>>>>>>         DT. Both EDK2 and u-boot append this node in DT.
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> I think this was a mistake tbh
>>>>>>>>>>>
>>>>>>>>>>>>         But above approach causes issue for ACPI since ACPI
>>>>>>>>>>>> initialization
>>>>>>>>>>>>         happens late in the proper kernel. Same is true even if we
>>>>>>>>>>>> pass this
>>>>>>>>>>>>         information via SMBIOS.
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
>>>>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
>>>>>>>>>>> pass
>>>>>>>>>>> it directly, without having to rely on firmware tables.
>>>>>>>>>>
>>>>>>>>>> As discovering the current process' hartid is not a UEFI specific
>>>>>>>>>> task
>>>>>>>>>> SBI would be a better fit.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
>>>>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
>>>>>>>>> pass in A0, it should use a EFI protocol and nothing else.
>>>>>>>>>
>>>>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
>>>>>>>>> calling into SBI is a different matter (and likely the best choice).
>>>>>>>>> But that does not mean the EFI stub should make SBI calls directly.
>>>>>>>>>
>>>>>>>>
>>>>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
>>>>>>>> that does. And that kernel already implements SBI calls.
>>>>>>>>
>>>>>>>> The main kernel could just try to read CSR mhartid which fails in
>>>>>>>> S-mode
>>>>>>>> and the SBI could emulate it.
>>>>>>>
>>>>>>> New SBI extension should be added only if there is no other way to
>>>>>>> solve a generic
>>>>>
>>>>> I am not sure this feature would be implemented as SBI extension or as a
>>>>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
>>>>> an update of the SBI specification.
>>>>>
>>>>>>> problem. The boot hartid issue is very specific to efi booting only.
>>>>>>> Any system that doesn't require
>>>>>
>>>>> The boot hartid is not EFI related at all. A firmware running single
>>>>> threaded does not need this information.
>>>>>
>>>>> Information about the boot hartid is a general OS need.
>>>>>
>>>>> I am wondering why S-mode software should not have a generic means to
>>>>> find out on which hart it is currently running.
>>>>>
>>>>>>> EFI booting won't need it. Even for EFI booting, we have other
>>>>>>> approaches already proposed
>>>>>>> to solve it. That's why, SBI extension should be the last resort
>>>>>>> rather than first.
>>>>>>>
>>>>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
>>>>>>> work for all the cases.
>>>>>>> Is there a case where you think it may not work ? U-Boot & EDK2
>>>>>>> already stores the boot hartid.
>>>>>>> They just implement that protocol and pass the hartid to the caller.
>>>>>>> We do need to support it in the grub though.
>>>>>>>
>>>>>>
>>>>>> Why would GRUB care about this? The EFI stub will call into the
>>>>>> underlying firmware to invoke the protocol, GRUB is just a loader with
>>>>>> a fancy menu that allows you to select which image to load, no?
>>>>>
>>>>> This is a related discussion:
>>>>>
>>>>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
>>>>>
>>>
>>> Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
>>> still debating the same topic :).
>>> Let me summarize the thread. There are multiple ways for EFI stub code
>>> to retrieve the boot hartid.
>>>
>>> 1. EFI variables - This is what Henerich proposed last time. Ard
>>> suggested that EFI configuration tables are better candidates than EFI
>>> variables.
>>> 2. DT modification - This was preferred over the configuration table
>>> at that time given because RISC-V was DT only at that time.
>>>                                    We already had all the infrastructure
>>> around DT. Thus, DT seemed to be a natural choice then.
>>>                                    It works now for existing setup
>>> however, the DT approach will not work for systems with ACPI support.
>>>                                    Adding a similar entry in ACPI tables
>>> is possible but adding ACPI support in EFI stub is not trivial.
>>> 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
>>> mandatory and adding SMBIOS support in EFI stub is not trivial.
>>> 4. SBI         -  As I mentioned before, this is an EFI specific
>>> problem because EFI stub doesn't know what the boot hartid is. Thus,
>>> it should be solved
>>>                         in an EFI specific way. An SBI extension for
>>> such features may not be acceptable as the non-EFI booting method
>>> works fine without the SBI extension.
>>> 5. RISC-V specific EFI configuration table or protocol: Ard suggested
>>> EFI configuration table last time. Earlier in this thread, EFI
>>> protocol was suggested.
>>>                         My personal preference has always been one of
>>> these as it solves the problem for all EFI booting methods
>>>                         for platforms-os
>>> combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
>>>
>>> @Heinrich: Do you see any issue with the EFI configuration table or
>>> protocol to retrieve the boot hartid?
>>
>> There is nothing technical stopping us from implementing either option.
>>
>> We could simply reuse the EFI Device Tree Fixup Protocol
>> (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
>> U-Boot and already used by systemd-boot. Pass a devicetree (which may be
>> empty) to the Fixup() method and it will add the /chosen node with the
>> boot-hartid parameter.
>>
>> The EFI stub anyway creates a new device-tree to pass the memory map to
>> the kernel in the ACPI case (function update_fdt()). Calling the EFI
>> Device Tree Fixup Protocol could be easily added.
> 
> Are you suggesting that DTB (skeletal or full-blown) will always be there when
> booting the kernel as an EFI application ? If yes then we are
> indirectly mandating
> skeletal DTB for UEFI+ACPI system.

The boot-hartid uses to be the hartid of the current thread. Are 
operating systems supposed to support boot-hartid to relate to another 
hardware thread then the current one? If the boot-hartid can differ from 
the current thread, what would be the source of truth? Is there any 
formal specification defining what the boot-hartid is and how it shall 
be used? Is there any formal specification which defines the transfer of 
the boot-hartid in the boot flow?

I only found this in the OpenSBI documentation:

The DT properties of a domain instance DT node are as follows:
* **boot-hart** (Optional) - The DT node phandle of the HART booting the 
domain instance. If coldboot HART is assigned to the domain instance 
then this DT property is ignored and the coldboot HART is assumed to be 
the boot HART of the domain instance.

The only piece of software that cares about the boot-hartid property is 
neither the SBI nor the UEFI firmware nor the EFI stub but the main OS 
kernel. Carrying the current hartid from boot stage to boot stage via 
register and DTB entry looks like a poor design decision. Instead of 
relying on a chain of transfers it would preferable that whoever in the 
boot chain wants to know the current hartid requests it from the source 
of truth.

The source of truth for the current hardware thread is the value of the 
mhartid CSR. Unfortunately this can only be read in M-mode. It could be 
made available via the SBI. I see no reason why the operating system or 
hypervisor should not see the hartid of a software thread at any time.

If we decide to make the current design more complex by using an EFI 
protocol, we have to decide if we want to reuse an existing one, or 
introduce a new one.

We already have an existing protocol in U-Boot which could do the job 
and which uses a dtb as transfer format. Internally OpenSBI, U-Boot and 
Linux always use a device-tree. But this does not hold true for other 
software like EDK II. We could instead define a new protocol which uses 
a uint64_t parameter and does not require support for the flattened 
devicetree format.

My preferred choice would be getting rid of multiple transfers and 
letting the piece of software that needs the information read the 
boot-hartid directly from wherever the source of truth is.

Best regards

Heinrich

> 
> Regards,
> Anup
> 
>>
>> Best regards
>>
>> Heinrich
>>
>>>
>>> My only concern with the RISC-V EFI protocol is that Ard suggested it
>>> doesn't need a modification in UEFI spec.
>>> Where should we document it in this case ? We can't document it in
>>> Linux or EBBR.
>>> Because, this is a protocol that server systems and other non-Linux OS
>>> will also use.
>>> We can define it in the RISC-V platform spec. But that's not the usual
>>> place where somebody will look for the definition of such protocol.
>>>
>>> Wouldn't it be better to standardize it in UEFI spec ? The UEFI spec
>>> already has ARCH specific protocols/config tables.
>>>
>>>>>
>>>>> If GRUB loads a devicetree it will anyway have to call into the firmware
>>>>> for fixups. These will include adding the boot-hartid.
>>>>>
>>>>>>
>>>>>>> @Heinrich Schuchardt
>>>>>>> I vaguely remember you proposed something similar when we discussed
>>>>>>> this first during FOSDEM.
>>>>>>> I can't recall why it was abandoned in favor of the DT approach which
>>>>>>> works. But,
>>>>>>> it is not an ideal solution considering RISC-V ACPI support is already
>>>>>>> on the way.
>>>>>>>
>>>>>>> Do you have a link to the older thread where this thing was discussed ?
>>>>>
>>>>> Unfortunately I cannot find anything.
>>>>
>>>> I assume Atish referred to this thread:
>>>>
>>>> https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/
>>>>
>>>> Best regards
>>>>
>>>> Heinrich
>>>>
>>>> _______________________________________________
>>>> linux-riscv mailing list
>>>> linux-riscv@lists.infradead.org
>>>> http://lists.infradead.org/mailman/listinfo/linux-riscv
>>>
>>>
>>>

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Re: Question regarding "boot-hartid" DT node

[Anup Patel]

On Sat, Dec 4, 2021 at 2:08 PM Heinrich Schuchardt
<heinrich.schuchardt@canonical.com> wrote:
>
>
>
> On 12/4/21 05:24, Anup Patel wrote:
> > On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
> > <heinrich.schuchardt@canonical.com> wrote:
> >>
> >>
> >>
> >> On 12/4/21 01:44, Atish Patra wrote:
> >>> On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> >>>>
> >>>> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> >>>>> On 12/3/21 11:13, Ard Biesheuvel wrote:
> >>>>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
> >>>>>>>
> >>>>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> >>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>>>>>
> >>>>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
> >>>>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> >>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>>>>>>>
> >>>>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
> >>>>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
> >>>>>>>>>>> wrote:
> >>>>>>>>>>>>
> >>>>>>>>>>>> Hi All,
> >>>>>>>>>>>>         I am starting this thread to discuss about the
> >>>>>>>>>>>> "boot-hartid" DT node
> >>>>>>>>>>>>         that is being used in RISC-V Linux EFI stub.
> >>>>>>>>>>>>
> >>>>>>>>>>>>         As you know, the boot Hart ID is passed in a0 register to
> >>>>>>>>>>>> the kernel
> >>>>>>>>>>>>         and hence there is actually no need to pass it via DT.
> >>>>>>>>>>>> However, since
> >>>>>>>>>>>>         EFI stub follows EFI application calling conventions, it
> >>>>>>>>>>>> needs to
> >>>>>>>>>>>>         know the boot Hart ID so that it can pass it to the proper
> >>>>>>>>>>>> kernel via
> >>>>>>>>>>>>         a0. For this issue, the solution was to add
> >>>>>>>>>>>> "/chosen/boot-hartid" in
> >>>>>>>>>>>>         DT. Both EDK2 and u-boot append this node in DT.
> >>>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>> I think this was a mistake tbh
> >>>>>>>>>>>
> >>>>>>>>>>>>         But above approach causes issue for ACPI since ACPI
> >>>>>>>>>>>> initialization
> >>>>>>>>>>>>         happens late in the proper kernel. Same is true even if we
> >>>>>>>>>>>> pass this
> >>>>>>>>>>>>         information via SMBIOS.
> >>>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
> >>>>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
> >>>>>>>>>>> pass
> >>>>>>>>>>> it directly, without having to rely on firmware tables.
> >>>>>>>>>>
> >>>>>>>>>> As discovering the current process' hartid is not a UEFI specific
> >>>>>>>>>> task
> >>>>>>>>>> SBI would be a better fit.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> >>>>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
> >>>>>>>>> pass in A0, it should use a EFI protocol and nothing else.
> >>>>>>>>>
> >>>>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
> >>>>>>>>> calling into SBI is a different matter (and likely the best choice).
> >>>>>>>>> But that does not mean the EFI stub should make SBI calls directly.
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> >>>>>>>> that does. And that kernel already implements SBI calls.
> >>>>>>>>
> >>>>>>>> The main kernel could just try to read CSR mhartid which fails in
> >>>>>>>> S-mode
> >>>>>>>> and the SBI could emulate it.
> >>>>>>>
> >>>>>>> New SBI extension should be added only if there is no other way to
> >>>>>>> solve a generic
> >>>>>
> >>>>> I am not sure this feature would be implemented as SBI extension or as a
> >>>>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
> >>>>> an update of the SBI specification.
> >>>>>
> >>>>>>> problem. The boot hartid issue is very specific to efi booting only.
> >>>>>>> Any system that doesn't require
> >>>>>
> >>>>> The boot hartid is not EFI related at all. A firmware running single
> >>>>> threaded does not need this information.
> >>>>>
> >>>>> Information about the boot hartid is a general OS need.
> >>>>>
> >>>>> I am wondering why S-mode software should not have a generic means to
> >>>>> find out on which hart it is currently running.
> >>>>>
> >>>>>>> EFI booting won't need it. Even for EFI booting, we have other
> >>>>>>> approaches already proposed
> >>>>>>> to solve it. That's why, SBI extension should be the last resort
> >>>>>>> rather than first.
> >>>>>>>
> >>>>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
> >>>>>>> work for all the cases.
> >>>>>>> Is there a case where you think it may not work ? U-Boot & EDK2
> >>>>>>> already stores the boot hartid.
> >>>>>>> They just implement that protocol and pass the hartid to the caller.
> >>>>>>> We do need to support it in the grub though.
> >>>>>>>
> >>>>>>
> >>>>>> Why would GRUB care about this? The EFI stub will call into the
> >>>>>> underlying firmware to invoke the protocol, GRUB is just a loader with
> >>>>>> a fancy menu that allows you to select which image to load, no?
> >>>>>
> >>>>> This is a related discussion:
> >>>>>
> >>>>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
> >>>>>
> >>>
> >>> Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
> >>> still debating the same topic :).
> >>> Let me summarize the thread. There are multiple ways for EFI stub code
> >>> to retrieve the boot hartid.
> >>>
> >>> 1. EFI variables - This is what Henerich proposed last time. Ard
> >>> suggested that EFI configuration tables are better candidates than EFI
> >>> variables.
> >>> 2. DT modification - This was preferred over the configuration table
> >>> at that time given because RISC-V was DT only at that time.
> >>>                                    We already had all the infrastructure
> >>> around DT. Thus, DT seemed to be a natural choice then.
> >>>                                    It works now for existing setup
> >>> however, the DT approach will not work for systems with ACPI support.
> >>>                                    Adding a similar entry in ACPI tables
> >>> is possible but adding ACPI support in EFI stub is not trivial.
> >>> 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
> >>> mandatory and adding SMBIOS support in EFI stub is not trivial.
> >>> 4. SBI         -  As I mentioned before, this is an EFI specific
> >>> problem because EFI stub doesn't know what the boot hartid is. Thus,
> >>> it should be solved
> >>>                         in an EFI specific way. An SBI extension for
> >>> such features may not be acceptable as the non-EFI booting method
> >>> works fine without the SBI extension.
> >>> 5. RISC-V specific EFI configuration table or protocol: Ard suggested
> >>> EFI configuration table last time. Earlier in this thread, EFI
> >>> protocol was suggested.
> >>>                         My personal preference has always been one of
> >>> these as it solves the problem for all EFI booting methods
> >>>                         for platforms-os
> >>> combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
> >>>
> >>> @Heinrich: Do you see any issue with the EFI configuration table or
> >>> protocol to retrieve the boot hartid?
> >>
> >> There is nothing technical stopping us from implementing either option.
> >>
> >> We could simply reuse the EFI Device Tree Fixup Protocol
> >> (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
> >> U-Boot and already used by systemd-boot. Pass a devicetree (which may be
> >> empty) to the Fixup() method and it will add the /chosen node with the
> >> boot-hartid parameter.
> >>
> >> The EFI stub anyway creates a new device-tree to pass the memory map to
> >> the kernel in the ACPI case (function update_fdt()). Calling the EFI
> >> Device Tree Fixup Protocol could be easily added.
> >
> > Are you suggesting that DTB (skeletal or full-blown) will always be there when
> > booting the kernel as an EFI application ? If yes then we are
> > indirectly mandating
> > skeletal DTB for UEFI+ACPI system.
>
> The boot-hartid uses to be the hartid of the current thread. Are
> operating systems supposed to support boot-hartid to relate to another
> hardware thread then the current one? If the boot-hartid can differ from
> the current thread, what would be the source of truth? Is there any

The boot-hartid is part of the boot protocol (non-EFI or EFI based).

For non-EFI based booting, the previous booting stage passes boot-hartid
in the a0 registers. This works perfectly fine and we don't have any issues
because OSes can save the boot-hartid from a0 register to some memory
location.

This issue of discovering boot-hartid only applies to EFI based booting
so we need a RISC-V specific protocol/configuration in EFI tables to allow
OSes to discover the boot-hartid.

> formal specification defining what the boot-hartid is and how it shall
> be used? Is there any formal specification which defines the transfer of
> the boot-hartid in the boot flow?

For non-EFI based booting, the "a0" register contains the hartid. This
convention has been followed in RISC-V since early days (10+ years).

EFI based booting is relatively new in the RISC-V world so this should
be solved in an EFI specific way.

>
> I only found this in the OpenSBI documentation:
>
> The DT properties of a domain instance DT node are as follows:
> * **boot-hart** (Optional) - The DT node phandle of the HART booting the
> domain instance. If coldboot HART is assigned to the domain instance
> then this DT property is ignored and the coldboot HART is assumed to be
> the boot HART of the domain instance.

This is not at all related to the problem we are discussing here. This
documentation talks about preferred boot-hart within a OpenSBI domain
and OpenSBI will remove the domain configuration details from DTB
before jumping to the next booting stage.

>
> The only piece of software that cares about the boot-hartid property is
> neither the SBI nor the UEFI firmware nor the EFI stub but the main OS
> kernel. Carrying the current hartid from boot stage to boot stage via
> register and DTB entry looks like a poor design decision. Instead of
> relying on a chain of transfers it would preferable that whoever in the
> boot chain wants to know the current hartid requests it from the source
> of truth.

Passing boot-hartid in DTB was a temporary decision (2 years back) when
Atish added EFI support in the kernel because back then there was no
ACPI support being developed for RISC-V kernel.

Now that we can have either DT or ACPI passed via EFI booting, we
need a EFI specific solution.

>
> The source of truth for the current hardware thread is the value of the
> mhartid CSR. Unfortunately this can only be read in M-mode. It could be
> made available via the SBI. I see no reason why the operating system or
> hypervisor should not see the hartid of a software thread at any time.

Both DT and ACPI have details of all HARTs along with their hartids, it's
only the boot-hartid (hartid of the booting HART) which needs to be known
to the kernel when booted as an EFI application.

Also, "boot-hartid" is a transient read-only information which is of no use
at runtime so defining an SBI call for this means has limited utility value:
1) It will be used only once for EFI based booting and never used at
runtime
2) Non-EFI booting will never use it because boot-hartid is available
in a0 register
3) Hypervisors which prefer booting kernel directly will never implement
it because it's redundant for such hypervisors

Clearly, "boot-hartid" needs to be part of the booting protocol and a SBI
call for this has very limited utility value.

>
> If we decide to make the current design more complex by using an EFI
> protocol, we have to decide if we want to reuse an existing one, or
> introduce a new one.
>
> We already have an existing protocol in U-Boot which could do the job
> and which uses a dtb as transfer format. Internally OpenSBI, U-Boot and
> Linux always use a device-tree. But this does not hold true for other
> software like EDK II. We could instead define a new protocol which uses
> a uint64_t parameter and does not require support for the flattened
> devicetree format.

Mandating some form of devicetree for EFI booting is a choice to be
made by the RISC-V platform specs.

>
> My preferred choice would be getting rid of multiple transfers and
> letting the piece of software that needs the information read the
> boot-hartid directly from wherever the source of truth is.

I disagree with this.

A SBI call just for determining boot-hartid is of limited utility (in this
case used only for EFI based booting). It is better to solve this problem
in a EFI specific way.

Regards,
Anup

>
> Best regards
>
> Heinrich
>
> >
> > Regards,
> > Anup
> >
> >>
> >> Best regards
> >>
> >> Heinrich
> >>
> >>>
> >>> My only concern with the RISC-V EFI protocol is that Ard suggested it
> >>> doesn't need a modification in UEFI spec.
> >>> Where should we document it in this case ? We can't document it in
> >>> Linux or EBBR.
> >>> Because, this is a protocol that server systems and other non-Linux OS
> >>> will also use.
> >>> We can define it in the RISC-V platform spec. But that's not the usual
> >>> place where somebody will look for the definition of such protocol.
> >>>
> >>> Wouldn't it be better to standardize it in UEFI spec ? The UEFI spec
> >>> already has ARCH specific protocols/config tables.
> >>>
> >>>>>
> >>>>> If GRUB loads a devicetree it will anyway have to call into the firmware
> >>>>> for fixups. These will include adding the boot-hartid.
> >>>>>
> >>>>>>
> >>>>>>> @Heinrich Schuchardt
> >>>>>>> I vaguely remember you proposed something similar when we discussed
> >>>>>>> this first during FOSDEM.
> >>>>>>> I can't recall why it was abandoned in favor of the DT approach which
> >>>>>>> works. But,
> >>>>>>> it is not an ideal solution considering RISC-V ACPI support is already
> >>>>>>> on the way.
> >>>>>>>
> >>>>>>> Do you have a link to the older thread where this thing was discussed ?
> >>>>>
> >>>>> Unfortunately I cannot find anything.
> >>>>
> >>>> I assume Atish referred to this thread:
> >>>>
> >>>> https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/
> >>>>
> >>>> Best regards
> >>>>
> >>>> Heinrich
> >>>>
> >>>> _______________________________________________
> >>>> linux-riscv mailing list
> >>>> linux-riscv@lists.infradead.org
> >>>> http://lists.infradead.org/mailman/listinfo/linux-riscv
> >>>
> >>>
> >>>

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Re: Question regarding "boot-hartid" DT node

[Atish Patra]

On Fri, Dec 3, 2021 at 8:24 PM Anup Patel <anup@brainfault.org> wrote:
>
> On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
> <heinrich.schuchardt@canonical.com> wrote:
> >
> >
> >
> > On 12/4/21 01:44, Atish Patra wrote:
> > > On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> > >>
> > >> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> > >>> On 12/3/21 11:13, Ard Biesheuvel wrote:
> > >>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
> > >>>>>
> > >>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> > >>>>> <heinrich.schuchardt@canonical.com> wrote:
> > >>>>>>
> > >>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
> > >>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> > >>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> > >>>>>>>>
> > >>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
> > >>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
> > >>>>>>>>> wrote:
> > >>>>>>>>>>
> > >>>>>>>>>> Hi All,
> > >>>>>>>>>>        I am starting this thread to discuss about the
> > >>>>>>>>>> "boot-hartid" DT node
> > >>>>>>>>>>        that is being used in RISC-V Linux EFI stub.
> > >>>>>>>>>>
> > >>>>>>>>>>        As you know, the boot Hart ID is passed in a0 register to
> > >>>>>>>>>> the kernel
> > >>>>>>>>>>        and hence there is actually no need to pass it via DT.
> > >>>>>>>>>> However, since
> > >>>>>>>>>>        EFI stub follows EFI application calling conventions, it
> > >>>>>>>>>> needs to
> > >>>>>>>>>>        know the boot Hart ID so that it can pass it to the proper
> > >>>>>>>>>> kernel via
> > >>>>>>>>>>        a0. For this issue, the solution was to add
> > >>>>>>>>>> "/chosen/boot-hartid" in
> > >>>>>>>>>>        DT. Both EDK2 and u-boot append this node in DT.
> > >>>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>> I think this was a mistake tbh
> > >>>>>>>>>
> > >>>>>>>>>>        But above approach causes issue for ACPI since ACPI
> > >>>>>>>>>> initialization
> > >>>>>>>>>>        happens late in the proper kernel. Same is true even if we
> > >>>>>>>>>> pass this
> > >>>>>>>>>>        information via SMBIOS.
> > >>>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
> > >>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
> > >>>>>>>>> pass
> > >>>>>>>>> it directly, without having to rely on firmware tables.
> > >>>>>>>>
> > >>>>>>>> As discovering the current process' hartid is not a UEFI specific
> > >>>>>>>> task
> > >>>>>>>> SBI would be a better fit.
> > >>>>>>>>
> > >>>>>>>
> > >>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> > >>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
> > >>>>>>> pass in A0, it should use a EFI protocol and nothing else.
> > >>>>>>>
> > >>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
> > >>>>>>> calling into SBI is a different matter (and likely the best choice).
> > >>>>>>> But that does not mean the EFI stub should make SBI calls directly.
> > >>>>>>>
> > >>>>>>
> > >>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> > >>>>>> that does. And that kernel already implements SBI calls.
> > >>>>>>
> > >>>>>> The main kernel could just try to read CSR mhartid which fails in
> > >>>>>> S-mode
> > >>>>>> and the SBI could emulate it.
> > >>>>>
> > >>>>> New SBI extension should be added only if there is no other way to
> > >>>>> solve a generic
> > >>>
> > >>> I am not sure this feature would be implemented as SBI extension or as a
> > >>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
> > >>> an update of the SBI specification.
> > >>>
> > >>>>> problem. The boot hartid issue is very specific to efi booting only.
> > >>>>> Any system that doesn't require
> > >>>
> > >>> The boot hartid is not EFI related at all. A firmware running single
> > >>> threaded does not need this information.
> > >>>
> > >>> Information about the boot hartid is a general OS need.
> > >>>
> > >>> I am wondering why S-mode software should not have a generic means to
> > >>> find out on which hart it is currently running.
> > >>>
> > >>>>> EFI booting won't need it. Even for EFI booting, we have other
> > >>>>> approaches already proposed
> > >>>>> to solve it. That's why, SBI extension should be the last resort
> > >>>>> rather than first.
> > >>>>>
> > >>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
> > >>>>> work for all the cases.
> > >>>>> Is there a case where you think it may not work ? U-Boot & EDK2
> > >>>>> already stores the boot hartid.
> > >>>>> They just implement that protocol and pass the hartid to the caller.
> > >>>>> We do need to support it in the grub though.
> > >>>>>
> > >>>>
> > >>>> Why would GRUB care about this? The EFI stub will call into the
> > >>>> underlying firmware to invoke the protocol, GRUB is just a loader with
> > >>>> a fancy menu that allows you to select which image to load, no?
> > >>>
> > >>> This is a related discussion:
> > >>>
> > >>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
> > >>>
> > >
> > > Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
> > > still debating the same topic :).
> > > Let me summarize the thread. There are multiple ways for EFI stub code
> > > to retrieve the boot hartid.
> > >
> > > 1. EFI variables - This is what Henerich proposed last time. Ard
> > > suggested that EFI configuration tables are better candidates than EFI
> > > variables.
> > > 2. DT modification - This was preferred over the configuration table
> > > at that time given because RISC-V was DT only at that time.
> > >                                   We already had all the infrastructure
> > > around DT. Thus, DT seemed to be a natural choice then.
> > >                                   It works now for existing setup
> > > however, the DT approach will not work for systems with ACPI support.
> > >                                   Adding a similar entry in ACPI tables
> > > is possible but adding ACPI support in EFI stub is not trivial.
> > > 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
> > > mandatory and adding SMBIOS support in EFI stub is not trivial.
> > > 4. SBI         -  As I mentioned before, this is an EFI specific
> > > problem because EFI stub doesn't know what the boot hartid is. Thus,
> > > it should be solved
> > >                        in an EFI specific way. An SBI extension for
> > > such features may not be acceptable as the non-EFI booting method
> > > works fine without the SBI extension.
> > > 5. RISC-V specific EFI configuration table or protocol: Ard suggested
> > > EFI configuration table last time. Earlier in this thread, EFI
> > > protocol was suggested.
> > >                        My personal preference has always been one of
> > > these as it solves the problem for all EFI booting methods
> > >                        for platforms-os
> > > combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
> > >
> > > @Heinrich: Do you see any issue with the EFI configuration table or
> > > protocol to retrieve the boot hartid?
> >
> > There is nothing technical stopping us from implementing either option.
> >
> > We could simply reuse the EFI Device Tree Fixup Protocol
> > (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
> > U-Boot and already used by systemd-boot. Pass a devicetree (which may be
> > empty) to the Fixup() method and it will add the /chosen node with the
> > boot-hartid parameter.
> >
> > The EFI stub anyway creates a new device-tree to pass the memory map to
> > the kernel in the ACPI case (function update_fdt()). Calling the EFI
> > Device Tree Fixup Protocol could be easily added.

Thanks. Yes. We can solve the current problem for EFI stub in Linux.

>
> Are you suggesting that DTB (skeletal or full-blown) will always be there when
> booting the kernel as an EFI application ? If yes then we are
> indirectly mandating
> skeletal DTB for UEFI+ACPI system.

Yes. EFI Stub tries to find a fdt from the command line (not a
preferred method) or EFI configuration table[1]
(currently used for RISC-V systems). If it can't find a device tree,
it generates one [2]

[1] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/efi-stub.c#L231
[2] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/fdt.c#L58

However, we may still need to define the RISC-V EFI protocol to
support ACPI for other OS (FreeBSD) which doesn't have
a stub like loader that uses DT.

In that case, where should we document it ? UEFI spec or RISC-V platform spec ?

>
> Regards,
> Anup
>
> >
> > Best regards
> >
> > Heinrich
> >
> > >
> > > My only concern with the RISC-V EFI protocol is that Ard suggested it
> > > doesn't need a modification in UEFI spec.
> > > Where should we document it in this case ? We can't document it in
> > > Linux or EBBR.
> > > Because, this is a protocol that server systems and other non-Linux OS
> > > will also use.
> > > We can define it in the RISC-V platform spec. But that's not the usual
> > > place where somebody will look for the definition of such protocol.
> > >
> > > Wouldn't it be better to standardize it in UEFI spec ? The UEFI spec
> > > already has ARCH specific protocols/config tables.
> > >
> > >>>
> > >>> If GRUB loads a devicetree it will anyway have to call into the firmware
> > >>> for fixups. These will include adding the boot-hartid.
> > >>>
> > >>>>
> > >>>>> @Heinrich Schuchardt
> > >>>>> I vaguely remember you proposed something similar when we discussed
> > >>>>> this first during FOSDEM.
> > >>>>> I can't recall why it was abandoned in favor of the DT approach which
> > >>>>> works. But,
> > >>>>> it is not an ideal solution considering RISC-V ACPI support is already
> > >>>>> on the way.
> > >>>>>
> > >>>>> Do you have a link to the older thread where this thing was discussed ?
> > >>>
> > >>> Unfortunately I cannot find anything.
> > >>
> > >> I assume Atish referred to this thread:
> > >>
> > >> https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/
> > >>
> > >> Best regards
> > >>
> > >> Heinrich
> > >>
> > >> _______________________________________________
> > >> linux-riscv mailing list
> > >> linux-riscv@lists.infradead.org
> > >> http://lists.infradead.org/mailman/listinfo/linux-riscv
> > >
> > >
> > >



-- 
Regards,
Atish

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Re: Question regarding "boot-hartid" DT node

[Heinrich Schuchardt]

On 12/4/21 19:34, Atish Patra wrote:
> On Fri, Dec 3, 2021 at 8:24 PM Anup Patel <anup@brainfault.org> wrote:
>>
>> On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
>> <heinrich.schuchardt@canonical.com> wrote:
>>>
>>>
>>>
>>> On 12/4/21 01:44, Atish Patra wrote:
>>>> On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
>>>>>
>>>>> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
>>>>>> On 12/3/21 11:13, Ard Biesheuvel wrote:
>>>>>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
>>>>>>>>
>>>>>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>>>>>
>>>>>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
>>>>>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
>>>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
>>>>>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>> Hi All,
>>>>>>>>>>>>>         I am starting this thread to discuss about the
>>>>>>>>>>>>> "boot-hartid" DT node
>>>>>>>>>>>>>         that is being used in RISC-V Linux EFI stub.
>>>>>>>>>>>>>
>>>>>>>>>>>>>         As you know, the boot Hart ID is passed in a0 register to
>>>>>>>>>>>>> the kernel
>>>>>>>>>>>>>         and hence there is actually no need to pass it via DT.
>>>>>>>>>>>>> However, since
>>>>>>>>>>>>>         EFI stub follows EFI application calling conventions, it
>>>>>>>>>>>>> needs to
>>>>>>>>>>>>>         know the boot Hart ID so that it can pass it to the proper
>>>>>>>>>>>>> kernel via
>>>>>>>>>>>>>         a0. For this issue, the solution was to add
>>>>>>>>>>>>> "/chosen/boot-hartid" in
>>>>>>>>>>>>>         DT. Both EDK2 and u-boot append this node in DT.
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> I think this was a mistake tbh
>>>>>>>>>>>>
>>>>>>>>>>>>>         But above approach causes issue for ACPI since ACPI
>>>>>>>>>>>>> initialization
>>>>>>>>>>>>>         happens late in the proper kernel. Same is true even if we
>>>>>>>>>>>>> pass this
>>>>>>>>>>>>>         information via SMBIOS.
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
>>>>>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
>>>>>>>>>>>> pass
>>>>>>>>>>>> it directly, without having to rely on firmware tables.
>>>>>>>>>>>
>>>>>>>>>>> As discovering the current process' hartid is not a UEFI specific
>>>>>>>>>>> task
>>>>>>>>>>> SBI would be a better fit.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
>>>>>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
>>>>>>>>>> pass in A0, it should use a EFI protocol and nothing else.
>>>>>>>>>>
>>>>>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
>>>>>>>>>> calling into SBI is a different matter (and likely the best choice).
>>>>>>>>>> But that does not mean the EFI stub should make SBI calls directly.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
>>>>>>>>> that does. And that kernel already implements SBI calls.
>>>>>>>>>
>>>>>>>>> The main kernel could just try to read CSR mhartid which fails in
>>>>>>>>> S-mode
>>>>>>>>> and the SBI could emulate it.
>>>>>>>>
>>>>>>>> New SBI extension should be added only if there is no other way to
>>>>>>>> solve a generic
>>>>>>
>>>>>> I am not sure this feature would be implemented as SBI extension or as a
>>>>>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
>>>>>> an update of the SBI specification.
>>>>>>
>>>>>>>> problem. The boot hartid issue is very specific to efi booting only.
>>>>>>>> Any system that doesn't require
>>>>>>
>>>>>> The boot hartid is not EFI related at all. A firmware running single
>>>>>> threaded does not need this information.
>>>>>>
>>>>>> Information about the boot hartid is a general OS need.
>>>>>>
>>>>>> I am wondering why S-mode software should not have a generic means to
>>>>>> find out on which hart it is currently running.
>>>>>>
>>>>>>>> EFI booting won't need it. Even for EFI booting, we have other
>>>>>>>> approaches already proposed
>>>>>>>> to solve it. That's why, SBI extension should be the last resort
>>>>>>>> rather than first.
>>>>>>>>
>>>>>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
>>>>>>>> work for all the cases.
>>>>>>>> Is there a case where you think it may not work ? U-Boot & EDK2
>>>>>>>> already stores the boot hartid.
>>>>>>>> They just implement that protocol and pass the hartid to the caller.
>>>>>>>> We do need to support it in the grub though.
>>>>>>>>
>>>>>>>
>>>>>>> Why would GRUB care about this? The EFI stub will call into the
>>>>>>> underlying firmware to invoke the protocol, GRUB is just a loader with
>>>>>>> a fancy menu that allows you to select which image to load, no?
>>>>>>
>>>>>> This is a related discussion:
>>>>>>
>>>>>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
>>>>>>
>>>>
>>>> Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
>>>> still debating the same topic :).
>>>> Let me summarize the thread. There are multiple ways for EFI stub code
>>>> to retrieve the boot hartid.
>>>>
>>>> 1. EFI variables - This is what Henerich proposed last time. Ard
>>>> suggested that EFI configuration tables are better candidates than EFI
>>>> variables.
>>>> 2. DT modification - This was preferred over the configuration table
>>>> at that time given because RISC-V was DT only at that time.
>>>>                                    We already had all the infrastructure
>>>> around DT. Thus, DT seemed to be a natural choice then.
>>>>                                    It works now for existing setup
>>>> however, the DT approach will not work for systems with ACPI support.
>>>>                                    Adding a similar entry in ACPI tables
>>>> is possible but adding ACPI support in EFI stub is not trivial.
>>>> 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
>>>> mandatory and adding SMBIOS support in EFI stub is not trivial.
>>>> 4. SBI         -  As I mentioned before, this is an EFI specific
>>>> problem because EFI stub doesn't know what the boot hartid is. Thus,
>>>> it should be solved
>>>>                         in an EFI specific way. An SBI extension for
>>>> such features may not be acceptable as the non-EFI booting method
>>>> works fine without the SBI extension.
>>>> 5. RISC-V specific EFI configuration table or protocol: Ard suggested
>>>> EFI configuration table last time. Earlier in this thread, EFI
>>>> protocol was suggested.
>>>>                         My personal preference has always been one of
>>>> these as it solves the problem for all EFI booting methods
>>>>                         for platforms-os
>>>> combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
>>>>
>>>> @Heinrich: Do you see any issue with the EFI configuration table or
>>>> protocol to retrieve the boot hartid?
>>>
>>> There is nothing technical stopping us from implementing either option.
>>>
>>> We could simply reuse the EFI Device Tree Fixup Protocol
>>> (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
>>> U-Boot and already used by systemd-boot. Pass a devicetree (which may be
>>> empty) to the Fixup() method and it will add the /chosen node with the
>>> boot-hartid parameter.
>>>
>>> The EFI stub anyway creates a new device-tree to pass the memory map to
>>> the kernel in the ACPI case (function update_fdt()). Calling the EFI
>>> Device Tree Fixup Protocol could be easily added.
> 
> Thanks. Yes. We can solve the current problem for EFI stub in Linux.
> 
>>
>> Are you suggesting that DTB (skeletal or full-blown) will always be there when
>> booting the kernel as an EFI application ? If yes then we are
>> indirectly mandating
>> skeletal DTB for UEFI+ACPI system.
> 
> Yes. EFI Stub tries to find a fdt from the command line (not a
> preferred method) or EFI configuration table[1]
> (currently used for RISC-V systems). If it can't find a device tree,
> it generates one [2]
> 
> [1] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/efi-stub.c#L231
> [2] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/fdt.c#L58
> 
> However, we may still need to define the RISC-V EFI protocol to
> support ACPI for other OS (FreeBSD) which doesn't have
> a stub like loader that uses DT.
> 
> In that case, where should we document it ? UEFI spec or RISC-V platform spec ?

Defining EFI protocols outside the UEFI spec has precedents, e.g. the 
EFI_TCG2_PROTOCOL is defined in a specification hosted by the Trusted 
Computing Group.

The UEFI Forum prefers an implemention first approach. We should 
demonstrate with a patched EDK II or U-Boot and a patched Linux that 
what we define is working before creating a change request.

Let's start with a draft protocol specification on Github and then 
develop the necessary patches.

Best regards

Heinrich

> 
>>
>> Regards,
>> Anup
>>
>>>
>>> Best regards
>>>
>>> Heinrich
>>>
>>>>
>>>> My only concern with the RISC-V EFI protocol is that Ard suggested it
>>>> doesn't need a modification in UEFI spec.
>>>> Where should we document it in this case ? We can't document it in
>>>> Linux or EBBR.
>>>> Because, this is a protocol that server systems and other non-Linux OS
>>>> will also use.
>>>> We can define it in the RISC-V platform spec. But that's not the usual
>>>> place where somebody will look for the definition of such protocol.
>>>>
>>>> Wouldn't it be better to standardize it in UEFI spec ? The UEFI spec
>>>> already has ARCH specific protocols/config tables.
>>>>
>>>>>>
>>>>>> If GRUB loads a devicetree it will anyway have to call into the firmware
>>>>>> for fixups. These will include adding the boot-hartid.
>>>>>>
>>>>>>>
>>>>>>>> @Heinrich Schuchardt
>>>>>>>> I vaguely remember you proposed something similar when we discussed
>>>>>>>> this first during FOSDEM.
>>>>>>>> I can't recall why it was abandoned in favor of the DT approach which
>>>>>>>> works. But,
>>>>>>>> it is not an ideal solution considering RISC-V ACPI support is already
>>>>>>>> on the way.
>>>>>>>>
>>>>>>>> Do you have a link to the older thread where this thing was discussed ?
>>>>>>
>>>>>> Unfortunately I cannot find anything.
>>>>>
>>>>> I assume Atish referred to this thread:
>>>>>
>>>>> https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/
>>>>>
>>>>> Best regards
>>>>>
>>>>> Heinrich
>>>>>
>>>>> _______________________________________________
>>>>> linux-riscv mailing list
>>>>> linux-riscv@lists.infradead.org
>>>>> http://lists.infradead.org/mailman/listinfo/linux-riscv
>>>>
>>>>
>>>>
> 
> 
> 

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Re: Question regarding "boot-hartid" DT node

[Ard Biesheuvel]

On Sat, 4 Dec 2021 at 20:03, Heinrich Schuchardt
<heinrich.schuchardt@canonical.com> wrote:
>
>
>
> On 12/4/21 19:34, Atish Patra wrote:
> > On Fri, Dec 3, 2021 at 8:24 PM Anup Patel <anup@brainfault.org> wrote:
> >>
> >> On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
> >> <heinrich.schuchardt@canonical.com> wrote:
> >>>
> >>>
> >>>
> >>> On 12/4/21 01:44, Atish Patra wrote:
> >>>> On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> >>>>>
> >>>>> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> >>>>>> On 12/3/21 11:13, Ard Biesheuvel wrote:
> >>>>>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
> >>>>>>>>
> >>>>>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> >>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>>>>>>
> >>>>>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
> >>>>>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> >>>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>>>>>>>>
> >>>>>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
> >>>>>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
> >>>>>>>>>>>> wrote:
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Hi All,
> >>>>>>>>>>>>>         I am starting this thread to discuss about the
> >>>>>>>>>>>>> "boot-hartid" DT node
> >>>>>>>>>>>>>         that is being used in RISC-V Linux EFI stub.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>         As you know, the boot Hart ID is passed in a0 register to
> >>>>>>>>>>>>> the kernel
> >>>>>>>>>>>>>         and hence there is actually no need to pass it via DT.
> >>>>>>>>>>>>> However, since
> >>>>>>>>>>>>>         EFI stub follows EFI application calling conventions, it
> >>>>>>>>>>>>> needs to
> >>>>>>>>>>>>>         know the boot Hart ID so that it can pass it to the proper
> >>>>>>>>>>>>> kernel via
> >>>>>>>>>>>>>         a0. For this issue, the solution was to add
> >>>>>>>>>>>>> "/chosen/boot-hartid" in
> >>>>>>>>>>>>>         DT. Both EDK2 and u-boot append this node in DT.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>
> >>>>>>>>>>>> I think this was a mistake tbh
> >>>>>>>>>>>>
> >>>>>>>>>>>>>         But above approach causes issue for ACPI since ACPI
> >>>>>>>>>>>>> initialization
> >>>>>>>>>>>>>         happens late in the proper kernel. Same is true even if we
> >>>>>>>>>>>>> pass this
> >>>>>>>>>>>>>         information via SMBIOS.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>
> >>>>>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
> >>>>>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
> >>>>>>>>>>>> pass
> >>>>>>>>>>>> it directly, without having to rely on firmware tables.
> >>>>>>>>>>>
> >>>>>>>>>>> As discovering the current process' hartid is not a UEFI specific
> >>>>>>>>>>> task
> >>>>>>>>>>> SBI would be a better fit.
> >>>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> >>>>>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
> >>>>>>>>>> pass in A0, it should use a EFI protocol and nothing else.
> >>>>>>>>>>
> >>>>>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
> >>>>>>>>>> calling into SBI is a different matter (and likely the best choice).
> >>>>>>>>>> But that does not mean the EFI stub should make SBI calls directly.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> >>>>>>>>> that does. And that kernel already implements SBI calls.
> >>>>>>>>>
> >>>>>>>>> The main kernel could just try to read CSR mhartid which fails in
> >>>>>>>>> S-mode
> >>>>>>>>> and the SBI could emulate it.
> >>>>>>>>
> >>>>>>>> New SBI extension should be added only if there is no other way to
> >>>>>>>> solve a generic
> >>>>>>
> >>>>>> I am not sure this feature would be implemented as SBI extension or as a
> >>>>>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
> >>>>>> an update of the SBI specification.
> >>>>>>
> >>>>>>>> problem. The boot hartid issue is very specific to efi booting only.
> >>>>>>>> Any system that doesn't require
> >>>>>>
> >>>>>> The boot hartid is not EFI related at all. A firmware running single
> >>>>>> threaded does not need this information.
> >>>>>>
> >>>>>> Information about the boot hartid is a general OS need.
> >>>>>>
> >>>>>> I am wondering why S-mode software should not have a generic means to
> >>>>>> find out on which hart it is currently running.
> >>>>>>
> >>>>>>>> EFI booting won't need it. Even for EFI booting, we have other
> >>>>>>>> approaches already proposed
> >>>>>>>> to solve it. That's why, SBI extension should be the last resort
> >>>>>>>> rather than first.
> >>>>>>>>
> >>>>>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
> >>>>>>>> work for all the cases.
> >>>>>>>> Is there a case where you think it may not work ? U-Boot & EDK2
> >>>>>>>> already stores the boot hartid.
> >>>>>>>> They just implement that protocol and pass the hartid to the caller.
> >>>>>>>> We do need to support it in the grub though.
> >>>>>>>>
> >>>>>>>
> >>>>>>> Why would GRUB care about this? The EFI stub will call into the
> >>>>>>> underlying firmware to invoke the protocol, GRUB is just a loader with
> >>>>>>> a fancy menu that allows you to select which image to load, no?
> >>>>>>
> >>>>>> This is a related discussion:
> >>>>>>
> >>>>>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
> >>>>>>
> >>>>
> >>>> Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
> >>>> still debating the same topic :).
> >>>> Let me summarize the thread. There are multiple ways for EFI stub code
> >>>> to retrieve the boot hartid.
> >>>>
> >>>> 1. EFI variables - This is what Henerich proposed last time. Ard
> >>>> suggested that EFI configuration tables are better candidates than EFI
> >>>> variables.
> >>>> 2. DT modification - This was preferred over the configuration table
> >>>> at that time given because RISC-V was DT only at that time.
> >>>>                                    We already had all the infrastructure
> >>>> around DT. Thus, DT seemed to be a natural choice then.
> >>>>                                    It works now for existing setup
> >>>> however, the DT approach will not work for systems with ACPI support.
> >>>>                                    Adding a similar entry in ACPI tables
> >>>> is possible but adding ACPI support in EFI stub is not trivial.
> >>>> 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
> >>>> mandatory and adding SMBIOS support in EFI stub is not trivial.
> >>>> 4. SBI         -  As I mentioned before, this is an EFI specific
> >>>> problem because EFI stub doesn't know what the boot hartid is. Thus,
> >>>> it should be solved
> >>>>                         in an EFI specific way. An SBI extension for
> >>>> such features may not be acceptable as the non-EFI booting method
> >>>> works fine without the SBI extension.
> >>>> 5. RISC-V specific EFI configuration table or protocol: Ard suggested
> >>>> EFI configuration table last time. Earlier in this thread, EFI
> >>>> protocol was suggested.
> >>>>                         My personal preference has always been one of
> >>>> these as it solves the problem for all EFI booting methods
> >>>>                         for platforms-os
> >>>> combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
> >>>>
> >>>> @Heinrich: Do you see any issue with the EFI configuration table or
> >>>> protocol to retrieve the boot hartid?
> >>>
> >>> There is nothing technical stopping us from implementing either option.
> >>>
> >>> We could simply reuse the EFI Device Tree Fixup Protocol
> >>> (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
> >>> U-Boot and already used by systemd-boot. Pass a devicetree (which may be
> >>> empty) to the Fixup() method and it will add the /chosen node with the
> >>> boot-hartid parameter.
> >>>
> >>> The EFI stub anyway creates a new device-tree to pass the memory map to
> >>> the kernel in the ACPI case (function update_fdt()). Calling the EFI
> >>> Device Tree Fixup Protocol could be easily added.
> >
> > Thanks. Yes. We can solve the current problem for EFI stub in Linux.
> >
> >>
> >> Are you suggesting that DTB (skeletal or full-blown) will always be there when
> >> booting the kernel as an EFI application ? If yes then we are
> >> indirectly mandating
> >> skeletal DTB for UEFI+ACPI system.
> >
> > Yes. EFI Stub tries to find a fdt from the command line (not a
> > preferred method) or EFI configuration table[1]
> > (currently used for RISC-V systems). If it can't find a device tree,
> > it generates one [2]
> >
> > [1] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/efi-stub.c#L231
> > [2] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/fdt.c#L58
> >
> > However, we may still need to define the RISC-V EFI protocol to
> > support ACPI for other OS (FreeBSD) which doesn't have
> > a stub like loader that uses DT.
> >
> > In that case, where should we document it ? UEFI spec or RISC-V platform spec ?
>
> Defining EFI protocols outside the UEFI spec has precedents, e.g. the
> EFI_TCG2_PROTOCOL is defined in a specification hosted by the Trusted
> Computing Group.
>

The 'E' in EFI means 'extensible' and the UEFI spec was never intended
as an exhaustive reference of all imaginable protocols. It is
perfectly fine to define your own protocols, and document them
wherever appropriate.

> The UEFI Forum prefers an implemention first approach. We should
> demonstrate with a patched EDK II or U-Boot and a patched Linux that
> what we define is working before creating a change request.
>

... if needed. There is no need to incorporate this into the UEFI spec.

> Let's start with a draft protocol specification on Github and then
> develop the necessary patches.
>

Agreed.

And to Heinrich's point regarding that there should not be a need for
this protocol: I completely agree. The fact that passing the
boot-hartid in a0 is part of the boot protocol is unfortunate, and
sadly, the EFI stub needs to implement what the boot protocol
stipulates, even though it is not a great design to begin with.

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Re: Question regarding "boot-hartid" DT node

[Sunil V L]

On Sat, Dec 04, 2021 at 10:34:28AM -0800, Atish Patra wrote:
> On Fri, Dec 3, 2021 at 8:24 PM Anup Patel <anup@brainfault.org> wrote:
> >
> > On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
> > <heinrich.schuchardt@canonical.com> wrote:
> > >
> > >
> > >
> > > On 12/4/21 01:44, Atish Patra wrote:
> > > > On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> > > >>
> > > >> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> > > >>> On 12/3/21 11:13, Ard Biesheuvel wrote:
> > > >>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
> > > >>>>>
> > > >>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> > > >>>>> <heinrich.schuchardt@canonical.com> wrote:
> > > >>>>>>
> > > >>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
> > > >>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> > > >>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> > > >>>>>>>>
> > > >>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
> > > >>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
> > > >>>>>>>>> wrote:
> > > >>>>>>>>>>
> > > >>>>>>>>>> Hi All,
> > > >>>>>>>>>>        I am starting this thread to discuss about the
> > > >>>>>>>>>> "boot-hartid" DT node
> > > >>>>>>>>>>        that is being used in RISC-V Linux EFI stub.
> > > >>>>>>>>>>
> > > >>>>>>>>>>        As you know, the boot Hart ID is passed in a0 register to
> > > >>>>>>>>>> the kernel
> > > >>>>>>>>>>        and hence there is actually no need to pass it via DT.
> > > >>>>>>>>>> However, since
> > > >>>>>>>>>>        EFI stub follows EFI application calling conventions, it
> > > >>>>>>>>>> needs to
> > > >>>>>>>>>>        know the boot Hart ID so that it can pass it to the proper
> > > >>>>>>>>>> kernel via
> > > >>>>>>>>>>        a0. For this issue, the solution was to add
> > > >>>>>>>>>> "/chosen/boot-hartid" in
> > > >>>>>>>>>>        DT. Both EDK2 and u-boot append this node in DT.
> > > >>>>>>>>>>
> > > >>>>>>>>>
> > > >>>>>>>>> I think this was a mistake tbh
> > > >>>>>>>>>
> > > >>>>>>>>>>        But above approach causes issue for ACPI since ACPI
> > > >>>>>>>>>> initialization
> > > >>>>>>>>>>        happens late in the proper kernel. Same is true even if we
> > > >>>>>>>>>> pass this
> > > >>>>>>>>>>        information via SMBIOS.
> > > >>>>>>>>>>
> > > >>>>>>>>>
> > > >>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
> > > >>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
> > > >>>>>>>>> pass
> > > >>>>>>>>> it directly, without having to rely on firmware tables.
> > > >>>>>>>>
> > > >>>>>>>> As discovering the current process' hartid is not a UEFI specific
> > > >>>>>>>> task
> > > >>>>>>>> SBI would be a better fit.
> > > >>>>>>>>
> > > >>>>>>>
> > > >>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> > > >>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
> > > >>>>>>> pass in A0, it should use a EFI protocol and nothing else.
> > > >>>>>>>
> > > >>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
> > > >>>>>>> calling into SBI is a different matter (and likely the best choice).
> > > >>>>>>> But that does not mean the EFI stub should make SBI calls directly.
> > > >>>>>>>
> > > >>>>>>
> > > >>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> > > >>>>>> that does. And that kernel already implements SBI calls.
> > > >>>>>>
> > > >>>>>> The main kernel could just try to read CSR mhartid which fails in
> > > >>>>>> S-mode
> > > >>>>>> and the SBI could emulate it.
> > > >>>>>
> > > >>>>> New SBI extension should be added only if there is no other way to
> > > >>>>> solve a generic
> > > >>>
> > > >>> I am not sure this feature would be implemented as SBI extension or as a
> > > >>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
> > > >>> an update of the SBI specification.
> > > >>>
> > > >>>>> problem. The boot hartid issue is very specific to efi booting only.
> > > >>>>> Any system that doesn't require
> > > >>>
> > > >>> The boot hartid is not EFI related at all. A firmware running single
> > > >>> threaded does not need this information.
> > > >>>
> > > >>> Information about the boot hartid is a general OS need.
> > > >>>
> > > >>> I am wondering why S-mode software should not have a generic means to
> > > >>> find out on which hart it is currently running.
> > > >>>
> > > >>>>> EFI booting won't need it. Even for EFI booting, we have other
> > > >>>>> approaches already proposed
> > > >>>>> to solve it. That's why, SBI extension should be the last resort
> > > >>>>> rather than first.
> > > >>>>>
> > > >>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
> > > >>>>> work for all the cases.
> > > >>>>> Is there a case where you think it may not work ? U-Boot & EDK2
> > > >>>>> already stores the boot hartid.
> > > >>>>> They just implement that protocol and pass the hartid to the caller.
> > > >>>>> We do need to support it in the grub though.
> > > >>>>>
> > > >>>>
> > > >>>> Why would GRUB care about this? The EFI stub will call into the
> > > >>>> underlying firmware to invoke the protocol, GRUB is just a loader with
> > > >>>> a fancy menu that allows you to select which image to load, no?
> > > >>>
> > > >>> This is a related discussion:
> > > >>>
> > > >>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
> > > >>>
> > > >
> > > > Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
> > > > still debating the same topic :).
> > > > Let me summarize the thread. There are multiple ways for EFI stub code
> > > > to retrieve the boot hartid.
> > > >
> > > > 1. EFI variables - This is what Henerich proposed last time. Ard
> > > > suggested that EFI configuration tables are better candidates than EFI
> > > > variables.
> > > > 2. DT modification - This was preferred over the configuration table
> > > > at that time given because RISC-V was DT only at that time.
> > > >                                   We already had all the infrastructure
> > > > around DT. Thus, DT seemed to be a natural choice then.
> > > >                                   It works now for existing setup
> > > > however, the DT approach will not work for systems with ACPI support.
> > > >                                   Adding a similar entry in ACPI tables
> > > > is possible but adding ACPI support in EFI stub is not trivial.
> > > > 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
> > > > mandatory and adding SMBIOS support in EFI stub is not trivial.
> > > > 4. SBI         -  As I mentioned before, this is an EFI specific
> > > > problem because EFI stub doesn't know what the boot hartid is. Thus,
> > > > it should be solved
> > > >                        in an EFI specific way. An SBI extension for
> > > > such features may not be acceptable as the non-EFI booting method
> > > > works fine without the SBI extension.
> > > > 5. RISC-V specific EFI configuration table or protocol: Ard suggested
> > > > EFI configuration table last time. Earlier in this thread, EFI
> > > > protocol was suggested.
> > > >                        My personal preference has always been one of
> > > > these as it solves the problem for all EFI booting methods
> > > >                        for platforms-os
> > > > combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
> > > >
> > > > @Heinrich: Do you see any issue with the EFI configuration table or
> > > > protocol to retrieve the boot hartid?
> > >
> > > There is nothing technical stopping us from implementing either option.
> > >
> > > We could simply reuse the EFI Device Tree Fixup Protocol
> > > (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
> > > U-Boot and already used by systemd-boot. Pass a devicetree (which may be
> > > empty) to the Fixup() method and it will add the /chosen node with the
> > > boot-hartid parameter.
> > >
> > > The EFI stub anyway creates a new device-tree to pass the memory map to
> > > the kernel in the ACPI case (function update_fdt()). Calling the EFI
> > > Device Tree Fixup Protocol could be easily added.
> 
> Thanks. Yes. We can solve the current problem for EFI stub in Linux.
> 
> >
> > Are you suggesting that DTB (skeletal or full-blown) will always be there when
> > booting the kernel as an EFI application ? If yes then we are
> > indirectly mandating
> > skeletal DTB for UEFI+ACPI system.
> 
> Yes. EFI Stub tries to find a fdt from the command line (not a
> preferred method) or EFI configuration table[1]
> (currently used for RISC-V systems). If it can't find a device tree,
> it generates one [2]
> 
> [1] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/efi-stub.c#L231
> [2] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/fdt.c#L58
> 
> However, we may still need to define the RISC-V EFI protocol to
> support ACPI for other OS (FreeBSD) which doesn't have
> a stub like loader that uses DT.
> 
If RISC-V mandates that every OS (including FreeBSD)  should follow the
booting protocol that a0 should be used to pass the boot hartid, then
only Linux EFI stub becomes a special case which can reuse the existing
DT based EFI protocol (mentioned by Heinrich), right?

Thanks
Sunil

> In that case, where should we document it ? UEFI spec or RISC-V platform spec ?
> 
> >
> > Regards,
> > Anup
> >
> > >
> > > Best regards
> > >
> > > Heinrich
> > >
> > > >
> > > > My only concern with the RISC-V EFI protocol is that Ard suggested it
> > > > doesn't need a modification in UEFI spec.
> > > > Where should we document it in this case ? We can't document it in
> > > > Linux or EBBR.
> > > > Because, this is a protocol that server systems and other non-Linux OS
> > > > will also use.
> > > > We can define it in the RISC-V platform spec. But that's not the usual
> > > > place where somebody will look for the definition of such protocol.
> > > >
> > > > Wouldn't it be better to standardize it in UEFI spec ? The UEFI spec
> > > > already has ARCH specific protocols/config tables.
> > > >
> > > >>>
> > > >>> If GRUB loads a devicetree it will anyway have to call into the firmware
> > > >>> for fixups. These will include adding the boot-hartid.
> > > >>>
> > > >>>>
> > > >>>>> @Heinrich Schuchardt
> > > >>>>> I vaguely remember you proposed something similar when we discussed
> > > >>>>> this first during FOSDEM.
> > > >>>>> I can't recall why it was abandoned in favor of the DT approach which
> > > >>>>> works. But,
> > > >>>>> it is not an ideal solution considering RISC-V ACPI support is already
> > > >>>>> on the way.
> > > >>>>>
> > > >>>>> Do you have a link to the older thread where this thing was discussed ?
> > > >>>
> > > >>> Unfortunately I cannot find anything.
> > > >>
> > > >> I assume Atish referred to this thread:
> > > >>
> > > >> https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/
> > > >>
> > > >> Best regards
> > > >>
> > > >> Heinrich
> > > >>
> > > >> _______________________________________________
> > > >> linux-riscv mailing list
> > > >> linux-riscv@lists.infradead.org
> > > >> http://lists.infradead.org/mailman/listinfo/linux-riscv
> > > >
> > > >
> > > >
> 
> 
> 
> -- 
> Regards,
> Atish

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Re: Question regarding "boot-hartid" DT node

[Jessica Clarke]

On 5 Dec 2021, at 13:39, Sunil V L <sunilvl@ventanamicro.com> wrote:
> 
> On Sat, Dec 04, 2021 at 10:34:28AM -0800, Atish Patra wrote:
>> On Fri, Dec 3, 2021 at 8:24 PM Anup Patel <anup@brainfault.org> wrote:
>>> 
>>> On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
>>> <heinrich.schuchardt@canonical.com> wrote:
>>>> 
>>>> 
>>>> 
>>>> On 12/4/21 01:44, Atish Patra wrote:
>>>>> On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
>>>>>> 
>>>>>> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
>>>>>>> On 12/3/21 11:13, Ard Biesheuvel wrote:
>>>>>>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
>>>>>>>>> 
>>>>>>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
>>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>>>>>> 
>>>>>>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
>>>>>>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
>>>>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
>>>>>>>>>>>> 
>>>>>>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
>>>>>>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>> 
>>>>>>>>>>>>>> Hi All,
>>>>>>>>>>>>>>       I am starting this thread to discuss about the
>>>>>>>>>>>>>> "boot-hartid" DT node
>>>>>>>>>>>>>>       that is being used in RISC-V Linux EFI stub.
>>>>>>>>>>>>>> 
>>>>>>>>>>>>>>       As you know, the boot Hart ID is passed in a0 register to
>>>>>>>>>>>>>> the kernel
>>>>>>>>>>>>>>       and hence there is actually no need to pass it via DT.
>>>>>>>>>>>>>> However, since
>>>>>>>>>>>>>>       EFI stub follows EFI application calling conventions, it
>>>>>>>>>>>>>> needs to
>>>>>>>>>>>>>>       know the boot Hart ID so that it can pass it to the proper
>>>>>>>>>>>>>> kernel via
>>>>>>>>>>>>>>       a0. For this issue, the solution was to add
>>>>>>>>>>>>>> "/chosen/boot-hartid" in
>>>>>>>>>>>>>>       DT. Both EDK2 and u-boot append this node in DT.
>>>>>>>>>>>>>> 
>>>>>>>>>>>>> 
>>>>>>>>>>>>> I think this was a mistake tbh
>>>>>>>>>>>>> 
>>>>>>>>>>>>>>       But above approach causes issue for ACPI since ACPI
>>>>>>>>>>>>>> initialization
>>>>>>>>>>>>>>       happens late in the proper kernel. Same is true even if we
>>>>>>>>>>>>>> pass this
>>>>>>>>>>>>>>       information via SMBIOS.
>>>>>>>>>>>>>> 
>>>>>>>>>>>>> 
>>>>>>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
>>>>>>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
>>>>>>>>>>>>> pass
>>>>>>>>>>>>> it directly, without having to rely on firmware tables.
>>>>>>>>>>>> 
>>>>>>>>>>>> As discovering the current process' hartid is not a UEFI specific
>>>>>>>>>>>> task
>>>>>>>>>>>> SBI would be a better fit.
>>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
>>>>>>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
>>>>>>>>>>> pass in A0, it should use a EFI protocol and nothing else.
>>>>>>>>>>> 
>>>>>>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
>>>>>>>>>>> calling into SBI is a different matter (and likely the best choice).
>>>>>>>>>>> But that does not mean the EFI stub should make SBI calls directly.
>>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
>>>>>>>>>> that does. And that kernel already implements SBI calls.
>>>>>>>>>> 
>>>>>>>>>> The main kernel could just try to read CSR mhartid which fails in
>>>>>>>>>> S-mode
>>>>>>>>>> and the SBI could emulate it.
>>>>>>>>> 
>>>>>>>>> New SBI extension should be added only if there is no other way to
>>>>>>>>> solve a generic
>>>>>>> 
>>>>>>> I am not sure this feature would be implemented as SBI extension or as a
>>>>>>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
>>>>>>> an update of the SBI specification.
>>>>>>> 
>>>>>>>>> problem. The boot hartid issue is very specific to efi booting only.
>>>>>>>>> Any system that doesn't require
>>>>>>> 
>>>>>>> The boot hartid is not EFI related at all. A firmware running single
>>>>>>> threaded does not need this information.
>>>>>>> 
>>>>>>> Information about the boot hartid is a general OS need.
>>>>>>> 
>>>>>>> I am wondering why S-mode software should not have a generic means to
>>>>>>> find out on which hart it is currently running.
>>>>>>> 
>>>>>>>>> EFI booting won't need it. Even for EFI booting, we have other
>>>>>>>>> approaches already proposed
>>>>>>>>> to solve it. That's why, SBI extension should be the last resort
>>>>>>>>> rather than first.
>>>>>>>>> 
>>>>>>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
>>>>>>>>> work for all the cases.
>>>>>>>>> Is there a case where you think it may not work ? U-Boot & EDK2
>>>>>>>>> already stores the boot hartid.
>>>>>>>>> They just implement that protocol and pass the hartid to the caller.
>>>>>>>>> We do need to support it in the grub though.
>>>>>>>>> 
>>>>>>>> 
>>>>>>>> Why would GRUB care about this? The EFI stub will call into the
>>>>>>>> underlying firmware to invoke the protocol, GRUB is just a loader with
>>>>>>>> a fancy menu that allows you to select which image to load, no?
>>>>>>> 
>>>>>>> This is a related discussion:
>>>>>>> 
>>>>>>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
>>>>>>> 
>>>>> 
>>>>> Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
>>>>> still debating the same topic :).
>>>>> Let me summarize the thread. There are multiple ways for EFI stub code
>>>>> to retrieve the boot hartid.
>>>>> 
>>>>> 1. EFI variables - This is what Henerich proposed last time. Ard
>>>>> suggested that EFI configuration tables are better candidates than EFI
>>>>> variables.
>>>>> 2. DT modification - This was preferred over the configuration table
>>>>> at that time given because RISC-V was DT only at that time.
>>>>>                                  We already had all the infrastructure
>>>>> around DT. Thus, DT seemed to be a natural choice then.
>>>>>                                  It works now for existing setup
>>>>> however, the DT approach will not work for systems with ACPI support.
>>>>>                                  Adding a similar entry in ACPI tables
>>>>> is possible but adding ACPI support in EFI stub is not trivial.
>>>>> 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
>>>>> mandatory and adding SMBIOS support in EFI stub is not trivial.
>>>>> 4. SBI         -  As I mentioned before, this is an EFI specific
>>>>> problem because EFI stub doesn't know what the boot hartid is. Thus,
>>>>> it should be solved
>>>>>                       in an EFI specific way. An SBI extension for
>>>>> such features may not be acceptable as the non-EFI booting method
>>>>> works fine without the SBI extension.
>>>>> 5. RISC-V specific EFI configuration table or protocol: Ard suggested
>>>>> EFI configuration table last time. Earlier in this thread, EFI
>>>>> protocol was suggested.
>>>>>                       My personal preference has always been one of
>>>>> these as it solves the problem for all EFI booting methods
>>>>>                       for platforms-os
>>>>> combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
>>>>> 
>>>>> @Heinrich: Do you see any issue with the EFI configuration table or
>>>>> protocol to retrieve the boot hartid?
>>>> 
>>>> There is nothing technical stopping us from implementing either option.
>>>> 
>>>> We could simply reuse the EFI Device Tree Fixup Protocol
>>>> (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
>>>> U-Boot and already used by systemd-boot. Pass a devicetree (which may be
>>>> empty) to the Fixup() method and it will add the /chosen node with the
>>>> boot-hartid parameter.
>>>> 
>>>> The EFI stub anyway creates a new device-tree to pass the memory map to
>>>> the kernel in the ACPI case (function update_fdt()). Calling the EFI
>>>> Device Tree Fixup Protocol could be easily added.
>> 
>> Thanks. Yes. We can solve the current problem for EFI stub in Linux.
>> 
>>> 
>>> Are you suggesting that DTB (skeletal or full-blown) will always be there when
>>> booting the kernel as an EFI application ? If yes then we are
>>> indirectly mandating
>>> skeletal DTB for UEFI+ACPI system.
>> 
>> Yes. EFI Stub tries to find a fdt from the command line (not a
>> preferred method) or EFI configuration table[1]
>> (currently used for RISC-V systems). If it can't find a device tree,
>> it generates one [2]
>> 
>> [1] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/efi-stub.c#L231
>> [2] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/fdt.c#L58
>> 
>> However, we may still need to define the RISC-V EFI protocol to
>> support ACPI for other OS (FreeBSD) which doesn't have
>> a stub like loader that uses DT.
>> 
> If RISC-V mandates that every OS (including FreeBSD)  should follow the
> booting protocol that a0 should be used to pass the boot hartid, then
> only Linux EFI stub becomes a special case which can reuse the existing
> DT based EFI protocol (mentioned by Heinrich), right?

Absolutely not. What you are saying is “let’s forbid anyone from using
UEFI”. This “booting protocol” thing is a RISC-V-specific low-level
interface that is incompatible with UEFI; in it, every architecture,
including RISC-V, passes exactly two arguments to the application, the
handle to the image and a pointer to the system table, and puts the
return address in the usual place. Linux’s EFI stub is not special;
*any* EFI application, be it your EFI stub, FreeBSD’s bootloader,
grub-efi, systemd-boot, OpenBSD’s bootloader, Haiku’s bootloader,
whatever, follows the UEFI spec and so does not, and never will, follow
the RISC-V booting protocol.

I wish everyone would stop talking about this “RISC-V booting
protocol”. It’s low-level firmware details that, due to not having a
mature firmware story at the time OSes were brought up, leaked up into
the OS booting process. In FreeBSD the only time it gets used is if the
kernel is booted directly from BBL/OpenSBI; if instead you boot the
bootloader via UEFI then that code is completely bypassed (and we make
the legacy direct boot method look like the bootloader method by
creating a “fake” bootloader metadata array, rather than the other way
round, which would be backwards and severely limiting). It’s not a good
protocol, OSes shouldn’t be using it, and it should fade into obscurity
outside of the M-mode firmware<->S-mode firmware interface. It’s just
not relevant to an OS. What is relevant is that there is critical
information in the firmware that the OS can’t get at if booting via the
industry-standard portable rich firmware interface, and that
information needs to be provided some way or another via a means
compatible with the specification. I like the SBI “get current hartid”
extension approach best, it’s the most flexible and there’s no harm in
having it exist in a crummy non-UEFI situation. It’s trivial to
implement, it’s trivial to use, it provides the interface that *should*
have existed in the ISA just like how mpidr_el1 is a thing on AArch64,
and it provides a way for even non-UEFI code to not have to care about
a0 being hartid (outside of perhaps the hart lottery in the entry point
if you need to support pre-HSM SBIs), it can just throw it away and ask
for it later when it needs it, just like if booting via UEFI. You could
also make it a UEFI protocol, but that’s more annoying to deal with,
you now have two different ways to get the same information depending
on how you were booted. You could also restrict it to only being “get
the boot hartid”, but why, what does that achieve? It doesn’t really
make it any simpler to implement, it’s just more restrictive for the
sake of being minimal, even if it is sufficient. But at the end of the
day all of them do work. So, please, can we stop wasting our lives on
this and just do *something* rather than going round and round in
circles and forgetting all the details in the process?

As for the “provide a dummy FDT to the proposed fixup protocol”
proposal, no, that’s clearly not going to fly with an ACPI-only OS that
doesn’t have, and never will include, a device tree parser. If your
ACPI system needs a device tree then it’s not ACPI-only any more.

Jess


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Re: Question regarding "boot-hartid" DT node

[Sunil V L]

On Sun, Dec 05, 2021 at 03:54:23PM +0000, Jessica Clarke wrote:
> On 5 Dec 2021, at 13:39, Sunil V L <sunilvl@ventanamicro.com> wrote:
> > 
> > On Sat, Dec 04, 2021 at 10:34:28AM -0800, Atish Patra wrote:
> >> On Fri, Dec 3, 2021 at 8:24 PM Anup Patel <anup@brainfault.org> wrote:
> >>> 
> >>> On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
> >>> <heinrich.schuchardt@canonical.com> wrote:
> >>>> 
> >>>> 
> >>>> 
> >>>> On 12/4/21 01:44, Atish Patra wrote:
> >>>>> On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> >>>>>> 
> >>>>>> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> >>>>>>> On 12/3/21 11:13, Ard Biesheuvel wrote:
> >>>>>>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
> >>>>>>>>> 
> >>>>>>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> >>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>>>>>>> 
> >>>>>>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
> >>>>>>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> >>>>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> >>>>>>>>>>>> 
> >>>>>>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
> >>>>>>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
> >>>>>>>>>>>>> wrote:
> >>>>>>>>>>>>>> 
> >>>>>>>>>>>>>> Hi All,
> >>>>>>>>>>>>>>       I am starting this thread to discuss about the
> >>>>>>>>>>>>>> "boot-hartid" DT node
> >>>>>>>>>>>>>>       that is being used in RISC-V Linux EFI stub.
> >>>>>>>>>>>>>> 
> >>>>>>>>>>>>>>       As you know, the boot Hart ID is passed in a0 register to
> >>>>>>>>>>>>>> the kernel
> >>>>>>>>>>>>>>       and hence there is actually no need to pass it via DT.
> >>>>>>>>>>>>>> However, since
> >>>>>>>>>>>>>>       EFI stub follows EFI application calling conventions, it
> >>>>>>>>>>>>>> needs to
> >>>>>>>>>>>>>>       know the boot Hart ID so that it can pass it to the proper
> >>>>>>>>>>>>>> kernel via
> >>>>>>>>>>>>>>       a0. For this issue, the solution was to add
> >>>>>>>>>>>>>> "/chosen/boot-hartid" in
> >>>>>>>>>>>>>>       DT. Both EDK2 and u-boot append this node in DT.
> >>>>>>>>>>>>>> 
> >>>>>>>>>>>>> 
> >>>>>>>>>>>>> I think this was a mistake tbh
> >>>>>>>>>>>>> 
> >>>>>>>>>>>>>>       But above approach causes issue for ACPI since ACPI
> >>>>>>>>>>>>>> initialization
> >>>>>>>>>>>>>>       happens late in the proper kernel. Same is true even if we
> >>>>>>>>>>>>>> pass this
> >>>>>>>>>>>>>>       information via SMBIOS.
> >>>>>>>>>>>>>> 
> >>>>>>>>>>>>> 
> >>>>>>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
> >>>>>>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
> >>>>>>>>>>>>> pass
> >>>>>>>>>>>>> it directly, without having to rely on firmware tables.
> >>>>>>>>>>>> 
> >>>>>>>>>>>> As discovering the current process' hartid is not a UEFI specific
> >>>>>>>>>>>> task
> >>>>>>>>>>>> SBI would be a better fit.
> >>>>>>>>>>>> 
> >>>>>>>>>>> 
> >>>>>>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> >>>>>>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
> >>>>>>>>>>> pass in A0, it should use a EFI protocol and nothing else.
> >>>>>>>>>>> 
> >>>>>>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
> >>>>>>>>>>> calling into SBI is a different matter (and likely the best choice).
> >>>>>>>>>>> But that does not mean the EFI stub should make SBI calls directly.
> >>>>>>>>>>> 
> >>>>>>>>>> 
> >>>>>>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> >>>>>>>>>> that does. And that kernel already implements SBI calls.
> >>>>>>>>>> 
> >>>>>>>>>> The main kernel could just try to read CSR mhartid which fails in
> >>>>>>>>>> S-mode
> >>>>>>>>>> and the SBI could emulate it.
> >>>>>>>>> 
> >>>>>>>>> New SBI extension should be added only if there is no other way to
> >>>>>>>>> solve a generic
> >>>>>>> 
> >>>>>>> I am not sure this feature would be implemented as SBI extension or as a
> >>>>>>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
> >>>>>>> an update of the SBI specification.
> >>>>>>> 
> >>>>>>>>> problem. The boot hartid issue is very specific to efi booting only.
> >>>>>>>>> Any system that doesn't require
> >>>>>>> 
> >>>>>>> The boot hartid is not EFI related at all. A firmware running single
> >>>>>>> threaded does not need this information.
> >>>>>>> 
> >>>>>>> Information about the boot hartid is a general OS need.
> >>>>>>> 
> >>>>>>> I am wondering why S-mode software should not have a generic means to
> >>>>>>> find out on which hart it is currently running.
> >>>>>>> 
> >>>>>>>>> EFI booting won't need it. Even for EFI booting, we have other
> >>>>>>>>> approaches already proposed
> >>>>>>>>> to solve it. That's why, SBI extension should be the last resort
> >>>>>>>>> rather than first.
> >>>>>>>>> 
> >>>>>>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
> >>>>>>>>> work for all the cases.
> >>>>>>>>> Is there a case where you think it may not work ? U-Boot & EDK2
> >>>>>>>>> already stores the boot hartid.
> >>>>>>>>> They just implement that protocol and pass the hartid to the caller.
> >>>>>>>>> We do need to support it in the grub though.
> >>>>>>>>> 
> >>>>>>>> 
> >>>>>>>> Why would GRUB care about this? The EFI stub will call into the
> >>>>>>>> underlying firmware to invoke the protocol, GRUB is just a loader with
> >>>>>>>> a fancy menu that allows you to select which image to load, no?
> >>>>>>> 
> >>>>>>> This is a related discussion:
> >>>>>>> 
> >>>>>>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
> >>>>>>> 
> >>>>> 
> >>>>> Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
> >>>>> still debating the same topic :).
> >>>>> Let me summarize the thread. There are multiple ways for EFI stub code
> >>>>> to retrieve the boot hartid.
> >>>>> 
> >>>>> 1. EFI variables - This is what Henerich proposed last time. Ard
> >>>>> suggested that EFI configuration tables are better candidates than EFI
> >>>>> variables.
> >>>>> 2. DT modification - This was preferred over the configuration table
> >>>>> at that time given because RISC-V was DT only at that time.
> >>>>>                                  We already had all the infrastructure
> >>>>> around DT. Thus, DT seemed to be a natural choice then.
> >>>>>                                  It works now for existing setup
> >>>>> however, the DT approach will not work for systems with ACPI support.
> >>>>>                                  Adding a similar entry in ACPI tables
> >>>>> is possible but adding ACPI support in EFI stub is not trivial.
> >>>>> 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
> >>>>> mandatory and adding SMBIOS support in EFI stub is not trivial.
> >>>>> 4. SBI         -  As I mentioned before, this is an EFI specific
> >>>>> problem because EFI stub doesn't know what the boot hartid is. Thus,
> >>>>> it should be solved
> >>>>>                       in an EFI specific way. An SBI extension for
> >>>>> such features may not be acceptable as the non-EFI booting method
> >>>>> works fine without the SBI extension.
> >>>>> 5. RISC-V specific EFI configuration table or protocol: Ard suggested
> >>>>> EFI configuration table last time. Earlier in this thread, EFI
> >>>>> protocol was suggested.
> >>>>>                       My personal preference has always been one of
> >>>>> these as it solves the problem for all EFI booting methods
> >>>>>                       for platforms-os
> >>>>> combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
> >>>>> 
> >>>>> @Heinrich: Do you see any issue with the EFI configuration table or
> >>>>> protocol to retrieve the boot hartid?
> >>>> 
> >>>> There is nothing technical stopping us from implementing either option.
> >>>> 
> >>>> We could simply reuse the EFI Device Tree Fixup Protocol
> >>>> (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
> >>>> U-Boot and already used by systemd-boot. Pass a devicetree (which may be
> >>>> empty) to the Fixup() method and it will add the /chosen node with the
> >>>> boot-hartid parameter.
> >>>> 
> >>>> The EFI stub anyway creates a new device-tree to pass the memory map to
> >>>> the kernel in the ACPI case (function update_fdt()). Calling the EFI
> >>>> Device Tree Fixup Protocol could be easily added.
> >> 
> >> Thanks. Yes. We can solve the current problem for EFI stub in Linux.
> >> 
> >>> 
> >>> Are you suggesting that DTB (skeletal or full-blown) will always be there when
> >>> booting the kernel as an EFI application ? If yes then we are
> >>> indirectly mandating
> >>> skeletal DTB for UEFI+ACPI system.
> >> 
> >> Yes. EFI Stub tries to find a fdt from the command line (not a
> >> preferred method) or EFI configuration table[1]
> >> (currently used for RISC-V systems). If it can't find a device tree,
> >> it generates one [2]
> >> 
> >> [1] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/efi-stub.c#L231
> >> [2] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/fdt.c#L58
> >> 
> >> However, we may still need to define the RISC-V EFI protocol to
> >> support ACPI for other OS (FreeBSD) which doesn't have
> >> a stub like loader that uses DT.
> >> 
> > If RISC-V mandates that every OS (including FreeBSD)  should follow the
> > booting protocol that a0 should be used to pass the boot hartid, then
> > only Linux EFI stub becomes a special case which can reuse the existing
> > DT based EFI protocol (mentioned by Heinrich), right?
> 
> Absolutely not. What you are saying is “let’s forbid anyone from using
> UEFI”. This “booting protocol” thing is a RISC-V-specific low-level
> interface that is incompatible with UEFI; in it, every architecture,
> including RISC-V, passes exactly two arguments to the application, the
> handle to the image and a pointer to the system table, and puts the
> return address in the usual place. Linux’s EFI stub is not special;
> *any* EFI application, be it your EFI stub, FreeBSD’s bootloader,
> grub-efi, systemd-boot, OpenBSD’s bootloader, Haiku’s bootloader,
> whatever, follows the UEFI spec and so does not, and never will, follow
> the RISC-V booting protocol.
> 
Yes, understood. Thanks!.

> I wish everyone would stop talking about this “RISC-V booting
> protocol”. It’s low-level firmware details that, due to not having a
> mature firmware story at the time OSes were brought up, leaked up into
> the OS booting process. In FreeBSD the only time it gets used is if the
> kernel is booted directly from BBL/OpenSBI; if instead you boot the
> bootloader via UEFI then that code is completely bypassed (and we make
> the legacy direct boot method look like the bootloader method by
> creating a “fake” bootloader metadata array, rather than the other way
> round, which would be backwards and severely limiting). It’s not a good
> protocol, OSes shouldn’t be using it, and it should fade into obscurity
> outside of the M-mode firmware<->S-mode firmware interface. It’s just
> not relevant to an OS. What is relevant is that there is critical
> information in the firmware that the OS can’t get at if booting via the
> industry-standard portable rich firmware interface, and that
> information needs to be provided some way or another via a means
> compatible with the specification. I like the SBI “get current hartid”
> extension approach best, it’s the most flexible and there’s no harm in
> having it exist in a crummy non-UEFI situation. It’s trivial to
> implement, it’s trivial to use, it provides the interface that *should*
> have existed in the ISA just like how mpidr_el1 is a thing on AArch64,
> and it provides a way for even non-UEFI code to not have to care about
> a0 being hartid (outside of perhaps the hart lottery in the entry point
> if you need to support pre-HSM SBIs), it can just throw it away and ask
> for it later when it needs it, just like if booting via UEFI. You could
> also make it a UEFI protocol, but that’s more annoying to deal with,
> you now have two different ways to get the same information depending
> on how you were booted. You could also restrict it to only being “get
> the boot hartid”, but why, what does that achieve? It doesn’t really
> make it any simpler to implement, it’s just more restrictive for the
> sake of being minimal, even if it is sufficient. But at the end of the
> day all of them do work. So, please, can we stop wasting our lives on
> this and just do *something* rather than going round and round in
> circles and forgetting all the details in the process?
> 
> As for the “provide a dummy FDT to the proposed fixup protocol”
> proposal, no, that’s clearly not going to fly with an ACPI-only OS that
> doesn’t have, and never will include, a device tree parser. If your
> ACPI system needs a device tree then it’s not ACPI-only any more.
> 
Completely agree.

I can draft the EFI protocol but I also feel "SBI interface to get
current hartid" is better. Considering that the software ecosystem is
expanding for risc-v, this will cater to any future needs. I am
concerned that this EFI protocol will be of no use if SBI implements
"get current hart id" in future.

Thanks
Sunil

> Jess
> 

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Re: Question regarding "boot-hartid" DT node

[Sunil V L]

On Sun, Dec 05, 2021 at 02:21:34PM -0800, Atish Patra wrote:
> On Sun, Dec 5, 2021 at 8:38 AM Sunil V L <sunilvl@ventanamicro.com> wrote:
> 
> > On Sun, Dec 05, 2021 at 03:54:23PM +0000, Jessica Clarke wrote:
> > > On 5 Dec 2021, at 13:39, Sunil V L <sunilvl@ventanamicro.com> wrote:
> > > >
> > > > On Sat, Dec 04, 2021 at 10:34:28AM -0800, Atish Patra wrote:
> > > >> On Fri, Dec 3, 2021 at 8:24 PM Anup Patel <anup@brainfault.org>
> > wrote:
> > > >>>
> > > >>> On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
> > > >>> <heinrich.schuchardt@canonical.com> wrote:
> > > >>>>
> > > >>>>
> > > >>>>
> > > >>>> On 12/4/21 01:44, Atish Patra wrote:
> > > >>>>> On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <
> > xypron.glpk@gmx.de> wrote:
> > > >>>>>>
> > > >>>>>> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> > > >>>>>>> On 12/3/21 11:13, Ard Biesheuvel wrote:
> > > >>>>>>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org>
> > wrote:
> > > >>>>>>>>>
> > > >>>>>>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> > > >>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> > > >>>>>>>>>>
> > > >>>>>>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
> > > >>>>>>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> > > >>>>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> > > >>>>>>>>>>>>
> > > >>>>>>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
> > > >>>>>>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <
> > sunilvl@ventanamicro.com>
> > > >>>>>>>>>>>>> wrote:
> > > >>>>>>>>>>>>>>
> > > >>>>>>>>>>>>>> Hi All,
> > > >>>>>>>>>>>>>>       I am starting this thread to discuss about the
> > > >>>>>>>>>>>>>> "boot-hartid" DT node
> > > >>>>>>>>>>>>>>       that is being used in RISC-V Linux EFI stub.
> > > >>>>>>>>>>>>>>
> > > >>>>>>>>>>>>>>       As you know, the boot Hart ID is passed in a0
> > register to
> > > >>>>>>>>>>>>>> the kernel
> > > >>>>>>>>>>>>>>       and hence there is actually no need to pass it via
> > DT.
> > > >>>>>>>>>>>>>> However, since
> > > >>>>>>>>>>>>>>       EFI stub follows EFI application calling
> > conventions, it
> > > >>>>>>>>>>>>>> needs to
> > > >>>>>>>>>>>>>>       know the boot Hart ID so that it can pass it to the
> > proper
> > > >>>>>>>>>>>>>> kernel via
> > > >>>>>>>>>>>>>>       a0. For this issue, the solution was to add
> > > >>>>>>>>>>>>>> "/chosen/boot-hartid" in
> > > >>>>>>>>>>>>>>       DT. Both EDK2 and u-boot append this node in DT.
> > > >>>>>>>>>>>>>>
> > > >>>>>>>>>>>>>
> > > >>>>>>>>>>>>> I think this was a mistake tbh
> > > >>>>>>>>>>>>>
> > > >>>>>>>>>>>>>>       But above approach causes issue for ACPI since ACPI
> > > >>>>>>>>>>>>>> initialization
> > > >>>>>>>>>>>>>>       happens late in the proper kernel. Same is true
> > even if we
> > > >>>>>>>>>>>>>> pass this
> > > >>>>>>>>>>>>>>       information via SMBIOS.
> > > >>>>>>>>>>>>>>
> > > >>>>>>>>>>>>>
> > > >>>>>>>>>>>>> It would be better to define a RISCV specific EFI protocol
> > that the
> > > >>>>>>>>>>>>> stub can call to discover the boot-hartid value. That wat,
> > it can
> > > >>>>>>>>>>>>> pass
> > > >>>>>>>>>>>>> it directly, without having to rely on firmware tables.
> > > >>>>>>>>>>>>
> > > >>>>>>>>>>>> As discovering the current process' hartid is not a UEFI
> > specific
> > > >>>>>>>>>>>> task
> > > >>>>>>>>>>>> SBI would be a better fit.
> > > >>>>>>>>>>>>
> > > >>>>>>>>>>>
> > > >>>>>>>>>>> I disagree. The OS<->loader firmware interface is UEFI not
> > SBI. So if
> > > >>>>>>>>>>> the EFI stub needs to ask the firmware which boot-hartid it
> > should
> > > >>>>>>>>>>> pass in A0, it should use a EFI protocol and nothing else.
> > > >>>>>>>>>>>
> > > >>>>>>>>>>> Whether or not the loader/firmware *implements* this EFI
> > protocol by
> > > >>>>>>>>>>> calling into SBI is a different matter (and likely the best
> > choice).
> > > >>>>>>>>>>> But that does not mean the EFI stub should make SBI calls
> > directly.
> > > >>>>>>>>>>>
> > > >>>>>>>>>>
> > > >>>>>>>>>> The EFI stub does not need the boot-hartid. It is the main
> > Linux kernel
> > > >>>>>>>>>> that does. And that kernel already implements SBI calls.
> > > >>>>>>>>>>
> > > >>>>>>>>>> The main kernel could just try to read CSR mhartid which
> > fails in
> > > >>>>>>>>>> S-mode
> > > >>>>>>>>>> and the SBI could emulate it.
> > > >>>>>>>>>
> > > >>>>>>>>> New SBI extension should be added only if there is no other
> > way to
> > > >>>>>>>>> solve a generic
> > > >>>>>>>
> > > >>>>>>> I am not sure this feature would be implemented as SBI extension
> > or as a
> > > >>>>>>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would
> > require
> > > >>>>>>> an update of the SBI specification.
> > > >>>>>>>
> > > >>>>>>>>> problem. The boot hartid issue is very specific to efi booting
> > only.
> > > >>>>>>>>> Any system that doesn't require
> > > >>>>>>>
> > > >>>>>>> The boot hartid is not EFI related at all. A firmware running
> > single
> > > >>>>>>> threaded does not need this information.
> > > >>>>>>>
> > > >>>>>>> Information about the boot hartid is a general OS need.
> > > >>>>>>>
> > > >>>>>>> I am wondering why S-mode software should not have a generic
> > means to
> > > >>>>>>> find out on which hart it is currently running.
> > > >>>>>>>
> > > >>>>>>>>> EFI booting won't need it. Even for EFI booting, we have other
> > > >>>>>>>>> approaches already proposed
> > > >>>>>>>>> to solve it. That's why, SBI extension should be the last
> > resort
> > > >>>>>>>>> rather than first.
> > > >>>>>>>>>
> > > >>>>>>>>> I think an RISC-V specific EFI protocol as suggested by Ard
> > should
> > > >>>>>>>>> work for all the cases.
> > > >>>>>>>>> Is there a case where you think it may not work ? U-Boot & EDK2
> > > >>>>>>>>> already stores the boot hartid.
> > > >>>>>>>>> They just implement that protocol and pass the hartid to the
> > caller.
> > > >>>>>>>>> We do need to support it in the grub though.
> > > >>>>>>>>>
> > > >>>>>>>>
> > > >>>>>>>> Why would GRUB care about this? The EFI stub will call into the
> > > >>>>>>>> underlying firmware to invoke the protocol, GRUB is just a
> > loader with
> > > >>>>>>>> a fancy menu that allows you to select which image to load, no?
> > > >>>>>>>
> > > >>>>>>> This is a related discussion:
> > > >>>>>>>
> > > >>>>>>>
> > https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
> > > >>>>>>>
> > > >>>>>
> > > >>>>> Yes!! Thanks for refreshing the memory. It seems after 2 years, we
> > are
> > > >>>>> still debating the same topic :).
> > > >>>>> Let me summarize the thread. There are multiple ways for EFI stub
> > code
> > > >>>>> to retrieve the boot hartid.
> > > >>>>>
> > > >>>>> 1. EFI variables - This is what Henerich proposed last time. Ard
> > > >>>>> suggested that EFI configuration tables are better candidates than
> > EFI
> > > >>>>> variables.
> > > >>>>> 2. DT modification - This was preferred over the configuration
> > table
> > > >>>>> at that time given because RISC-V was DT only at that time.
> > > >>>>>                                  We already had all the
> > infrastructure
> > > >>>>> around DT. Thus, DT seemed to be a natural choice then.
> > > >>>>>                                  It works now for existing setup
> > > >>>>> however, the DT approach will not work for systems with ACPI
> > support.
> > > >>>>>                                  Adding a similar entry in ACPI
> > tables
> > > >>>>> is possible but adding ACPI support in EFI stub is not trivial.
> > > >>>>> 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
> > > >>>>> mandatory and adding SMBIOS support in EFI stub is not trivial.
> > > >>>>> 4. SBI         -  As I mentioned before, this is an EFI specific
> > > >>>>> problem because EFI stub doesn't know what the boot hartid is.
> > Thus,
> > > >>>>> it should be solved
> > > >>>>>                       in an EFI specific way. An SBI extension for
> > > >>>>> such features may not be acceptable as the non-EFI booting method
> > > >>>>> works fine without the SBI extension.
> > > >>>>> 5. RISC-V specific EFI configuration table or protocol: Ard
> > suggested
> > > >>>>> EFI configuration table last time. Earlier in this thread, EFI
> > > >>>>> protocol was suggested.
> > > >>>>>                       My personal preference has always been one of
> > > >>>>> these as it solves the problem for all EFI booting methods
> > > >>>>>                       for platforms-os
> > > >>>>> combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
> > > >>>>>
> > > >>>>> @Heinrich: Do you see any issue with the EFI configuration table or
> > > >>>>> protocol to retrieve the boot hartid?
> > > >>>>
> > > >>>> There is nothing technical stopping us from implementing either
> > option.
> > > >>>>
> > > >>>> We could simply reuse the EFI Device Tree Fixup Protocol
> > > >>>> (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented
> > in
> > > >>>> U-Boot and already used by systemd-boot. Pass a devicetree (which
> > may be
> > > >>>> empty) to the Fixup() method and it will add the /chosen node with
> > the
> > > >>>> boot-hartid parameter.
> > > >>>>
> > > >>>> The EFI stub anyway creates a new device-tree to pass the memory
> > map to
> > > >>>> the kernel in the ACPI case (function update_fdt()). Calling the EFI
> > > >>>> Device Tree Fixup Protocol could be easily added.
> > > >>
> > > >> Thanks. Yes. We can solve the current problem for EFI stub in Linux.
> > > >>
> > > >>>
> > > >>> Are you suggesting that DTB (skeletal or full-blown) will always be
> > there when
> > > >>> booting the kernel as an EFI application ? If yes then we are
> > > >>> indirectly mandating
> > > >>> skeletal DTB for UEFI+ACPI system.
> > > >>
> > > >> Yes. EFI Stub tries to find a fdt from the command line (not a
> > > >> preferred method) or EFI configuration table[1]
> > > >> (currently used for RISC-V systems). If it can't find a device tree,
> > > >> it generates one [2]
> > > >>
> > > >> [1]
> > https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/efi-stub.c#L231
> > > >> [2]
> > https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/fdt.c#L58
> > > >>
> > > >> However, we may still need to define the RISC-V EFI protocol to
> > > >> support ACPI for other OS (FreeBSD) which doesn't have
> > > >> a stub like loader that uses DT.
> > > >>
> > > > If RISC-V mandates that every OS (including FreeBSD)  should follow the
> > > > booting protocol that a0 should be used to pass the boot hartid, then
> > > > only Linux EFI stub becomes a special case which can reuse the existing
> > > > DT based EFI protocol (mentioned by Heinrich), right?
> > >
> > > Absolutely not. What you are saying is “let’s forbid anyone from using
> > > UEFI”. This “booting protocol” thing is a RISC-V-specific low-level
> > > interface that is incompatible with UEFI; in it, every architecture,
> > > including RISC-V, passes exactly two arguments to the application, the
> > > handle to the image and a pointer to the system table, and puts the
> > > return address in the usual place. Linux’s EFI stub is not special;
> > > *any* EFI application, be it your EFI stub, FreeBSD’s bootloader,
> > > grub-efi, systemd-boot, OpenBSD’s bootloader, Haiku’s bootloader,
> > > whatever, follows the UEFI spec and so does not, and never will, follow
> > > the RISC-V booting protocol.
> > >
> > Yes, understood. Thanks!.
> >
> > > I wish everyone would stop talking about this “RISC-V booting
> > > protocol”. It’s low-level firmware details that, due to not having a
> > > mature firmware story at the time OSes were brought up, leaked up into
> > > the OS booting process. In FreeBSD the only time it gets used is if the
> > > kernel is booted directly from BBL/OpenSBI; if instead you boot the
> > > bootloader via UEFI then that code is completely bypassed (and we make
> > > the legacy direct boot method look like the bootloader method by
> > > creating a “fake” bootloader metadata array, rather than the other way
> > > round, which would be backwards and severely limiting). It’s not a good
> > > protocol, OSes shouldn’t be using it, and it should fade into obscurity
> > > outside of the M-mode firmware<->S-mode firmware interface. It’s just
> > > not relevant to an OS. What is relevant is that there is critical
> > > information in the firmware that the OS can’t get at if booting via the
> > > industry-standard portable rich firmware interface, and that
> > > information needs to be provided some way or another via a means
> > > compatible with the specification. I like the SBI “get current hartid”
> > > extension approach best, it’s the most flexible and there’s no harm in
> > > having it exist in a crummy non-UEFI situation. It’s trivial to
> > > implement, it’s trivial to use, it provides the interface that *should*
> > > have existed in the ISA just like how mpidr_el1 is a thing on AArch64,
> > > and it provides a way for even non-UEFI code to not have to care about
> > > a0 being hartid (outside of perhaps the hart lottery in the entry point
> > > if you need to support pre-HSM SBIs), it can just throw it away and ask
> > > for it later when it needs it, just like if booting via UEFI. You could
> > > also make it a UEFI protocol, but that’s more annoying to deal with,
> > > you now have two different ways to get the same information depending
> > > on how you were booted. You could also restrict it to only being “get
> > > the boot hartid”, but why, what does that achieve? It doesn’t really
> > > make it any simpler to implement, it’s just more restrictive for the
> > > sake of being minimal, even if it is sufficient. But at the end of the
> > > day all of them do work. So, please, can we stop wasting our lives on
> > > this and just do *something* rather than going round and round in
> > > circles and forgetting all the details in the process?
> > >
> > > As for the “provide a dummy FDT to the proposed fixup protocol”
> > > proposal, no, that’s clearly not going to fly with an ACPI-only OS that
> > > doesn’t have, and never will include, a device tree parser. If your
> > > ACPI system needs a device tree then it’s not ACPI-only any more.
> > >
> > Completely agree.
> >
> > I can draft the EFI protocol but I also feel "SBI interface to get
> > current hartid" is better. Considering that the software ecosystem is
> > expanding for risc-v, this will cater to any future needs. I am
> > concerned that this EFI protocol will be of no use if SBI implements
> > "get current hart id" in future.
> >
> 
> There won’t be an SBI extension for “get current hart id” for the reasons
> explained by earlier. So EFI protocol should be the way forward to solve
> this issue.
> 
Thank you Atish for that confirmation. Let me draft the EFI protocol
with a PoC and will request for review. We can decide where to host it
(RVI or UEFI spec) later.

Thank you all for your inputs. This was very helpful.

Thanks
Sunil
> 
> > Thanks
> > Sunil
> >
> > > Jess
> > >
> >
> -- 
> Regards,
> Atish

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Re: Question regarding "boot-hartid" DT node

[Sunil V L]

On Sat, Dec 04, 2021 at 08:13:35PM +0100, Ard Biesheuvel wrote:
> On Sat, 4 Dec 2021 at 20:03, Heinrich Schuchardt
> <heinrich.schuchardt@canonical.com> wrote:
> >
> >
> >
> > On 12/4/21 19:34, Atish Patra wrote:
> > > On Fri, Dec 3, 2021 at 8:24 PM Anup Patel <anup@brainfault.org> wrote:
> > >>
> > >> On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt
> > >> <heinrich.schuchardt@canonical.com> wrote:
> > >>>
> > >>>
> > >>>
> > >>> On 12/4/21 01:44, Atish Patra wrote:
> > >>>> On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> > >>>>>
> > >>>>> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote:
> > >>>>>> On 12/3/21 11:13, Ard Biesheuvel wrote:
> > >>>>>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra <atishp@atishpatra.org> wrote:
> > >>>>>>>>
> > >>>>>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt
> > >>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> > >>>>>>>>>
> > >>>>>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote:
> > >>>>>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt
> > >>>>>>>>>> <heinrich.schuchardt@canonical.com> wrote:
> > >>>>>>>>>>>
> > >>>>>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote:
> > >>>>>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L <sunilvl@ventanamicro.com>
> > >>>>>>>>>>>> wrote:
> > >>>>>>>>>>>>>
> > >>>>>>>>>>>>> Hi All,
> > >>>>>>>>>>>>>         I am starting this thread to discuss about the
> > >>>>>>>>>>>>> "boot-hartid" DT node
> > >>>>>>>>>>>>>         that is being used in RISC-V Linux EFI stub.
> > >>>>>>>>>>>>>
> > >>>>>>>>>>>>>         As you know, the boot Hart ID is passed in a0 register to
> > >>>>>>>>>>>>> the kernel
> > >>>>>>>>>>>>>         and hence there is actually no need to pass it via DT.
> > >>>>>>>>>>>>> However, since
> > >>>>>>>>>>>>>         EFI stub follows EFI application calling conventions, it
> > >>>>>>>>>>>>> needs to
> > >>>>>>>>>>>>>         know the boot Hart ID so that it can pass it to the proper
> > >>>>>>>>>>>>> kernel via
> > >>>>>>>>>>>>>         a0. For this issue, the solution was to add
> > >>>>>>>>>>>>> "/chosen/boot-hartid" in
> > >>>>>>>>>>>>>         DT. Both EDK2 and u-boot append this node in DT.
> > >>>>>>>>>>>>>
> > >>>>>>>>>>>>
> > >>>>>>>>>>>> I think this was a mistake tbh
> > >>>>>>>>>>>>
> > >>>>>>>>>>>>>         But above approach causes issue for ACPI since ACPI
> > >>>>>>>>>>>>> initialization
> > >>>>>>>>>>>>>         happens late in the proper kernel. Same is true even if we
> > >>>>>>>>>>>>> pass this
> > >>>>>>>>>>>>>         information via SMBIOS.
> > >>>>>>>>>>>>>
> > >>>>>>>>>>>>
> > >>>>>>>>>>>> It would be better to define a RISCV specific EFI protocol that the
> > >>>>>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can
> > >>>>>>>>>>>> pass
> > >>>>>>>>>>>> it directly, without having to rely on firmware tables.
> > >>>>>>>>>>>
> > >>>>>>>>>>> As discovering the current process' hartid is not a UEFI specific
> > >>>>>>>>>>> task
> > >>>>>>>>>>> SBI would be a better fit.
> > >>>>>>>>>>>
> > >>>>>>>>>>
> > >>>>>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if
> > >>>>>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should
> > >>>>>>>>>> pass in A0, it should use a EFI protocol and nothing else.
> > >>>>>>>>>>
> > >>>>>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by
> > >>>>>>>>>> calling into SBI is a different matter (and likely the best choice).
> > >>>>>>>>>> But that does not mean the EFI stub should make SBI calls directly.
> > >>>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel
> > >>>>>>>>> that does. And that kernel already implements SBI calls.
> > >>>>>>>>>
> > >>>>>>>>> The main kernel could just try to read CSR mhartid which fails in
> > >>>>>>>>> S-mode
> > >>>>>>>>> and the SBI could emulate it.
> > >>>>>>>>
> > >>>>>>>> New SBI extension should be added only if there is no other way to
> > >>>>>>>> solve a generic
> > >>>>>>
> > >>>>>> I am not sure this feature would be implemented as SBI extension or as a
> > >>>>>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require
> > >>>>>> an update of the SBI specification.
> > >>>>>>
> > >>>>>>>> problem. The boot hartid issue is very specific to efi booting only.
> > >>>>>>>> Any system that doesn't require
> > >>>>>>
> > >>>>>> The boot hartid is not EFI related at all. A firmware running single
> > >>>>>> threaded does not need this information.
> > >>>>>>
> > >>>>>> Information about the boot hartid is a general OS need.
> > >>>>>>
> > >>>>>> I am wondering why S-mode software should not have a generic means to
> > >>>>>> find out on which hart it is currently running.
> > >>>>>>
> > >>>>>>>> EFI booting won't need it. Even for EFI booting, we have other
> > >>>>>>>> approaches already proposed
> > >>>>>>>> to solve it. That's why, SBI extension should be the last resort
> > >>>>>>>> rather than first.
> > >>>>>>>>
> > >>>>>>>> I think an RISC-V specific EFI protocol as suggested by Ard should
> > >>>>>>>> work for all the cases.
> > >>>>>>>> Is there a case where you think it may not work ? U-Boot & EDK2
> > >>>>>>>> already stores the boot hartid.
> > >>>>>>>> They just implement that protocol and pass the hartid to the caller.
> > >>>>>>>> We do need to support it in the grub though.
> > >>>>>>>>
> > >>>>>>>
> > >>>>>>> Why would GRUB care about this? The EFI stub will call into the
> > >>>>>>> underlying firmware to invoke the protocol, GRUB is just a loader with
> > >>>>>>> a fancy menu that allows you to select which image to load, no?
> > >>>>>>
> > >>>>>> This is a related discussion:
> > >>>>>>
> > >>>>>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029
> > >>>>>>
> > >>>>
> > >>>> Yes!! Thanks for refreshing the memory. It seems after 2 years, we are
> > >>>> still debating the same topic :).
> > >>>> Let me summarize the thread. There are multiple ways for EFI stub code
> > >>>> to retrieve the boot hartid.
> > >>>>
> > >>>> 1. EFI variables - This is what Henerich proposed last time. Ard
> > >>>> suggested that EFI configuration tables are better candidates than EFI
> > >>>> variables.
> > >>>> 2. DT modification - This was preferred over the configuration table
> > >>>> at that time given because RISC-V was DT only at that time.
> > >>>>                                    We already had all the infrastructure
> > >>>> around DT. Thus, DT seemed to be a natural choice then.
> > >>>>                                    It works now for existing setup
> > >>>> however, the DT approach will not work for systems with ACPI support.
> > >>>>                                    Adding a similar entry in ACPI tables
> > >>>> is possible but adding ACPI support in EFI stub is not trivial.
> > >>>> 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not
> > >>>> mandatory and adding SMBIOS support in EFI stub is not trivial.
> > >>>> 4. SBI         -  As I mentioned before, this is an EFI specific
> > >>>> problem because EFI stub doesn't know what the boot hartid is. Thus,
> > >>>> it should be solved
> > >>>>                         in an EFI specific way. An SBI extension for
> > >>>> such features may not be acceptable as the non-EFI booting method
> > >>>> works fine without the SBI extension.
> > >>>> 5. RISC-V specific EFI configuration table or protocol: Ard suggested
> > >>>> EFI configuration table last time. Earlier in this thread, EFI
> > >>>> protocol was suggested.
> > >>>>                         My personal preference has always been one of
> > >>>> these as it solves the problem for all EFI booting methods
> > >>>>                         for platforms-os
> > >>>> combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way.
> > >>>>
> > >>>> @Heinrich: Do you see any issue with the EFI configuration table or
> > >>>> protocol to retrieve the boot hartid?
> > >>>
> > >>> There is nothing technical stopping us from implementing either option.
> > >>>
> > >>> We could simply reuse the EFI Device Tree Fixup Protocol
> > >>> (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in
> > >>> U-Boot and already used by systemd-boot. Pass a devicetree (which may be
> > >>> empty) to the Fixup() method and it will add the /chosen node with the
> > >>> boot-hartid parameter.
> > >>>
> > >>> The EFI stub anyway creates a new device-tree to pass the memory map to
> > >>> the kernel in the ACPI case (function update_fdt()). Calling the EFI
> > >>> Device Tree Fixup Protocol could be easily added.
> > >
> > > Thanks. Yes. We can solve the current problem for EFI stub in Linux.
> > >
> > >>
> > >> Are you suggesting that DTB (skeletal or full-blown) will always be there when
> > >> booting the kernel as an EFI application ? If yes then we are
> > >> indirectly mandating
> > >> skeletal DTB for UEFI+ACPI system.
> > >
> > > Yes. EFI Stub tries to find a fdt from the command line (not a
> > > preferred method) or EFI configuration table[1]
> > > (currently used for RISC-V systems). If it can't find a device tree,
> > > it generates one [2]
> > >
> > > [1] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/efi-stub.c#L231
> > > [2] https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/firmware/efi/libstub/fdt.c#L58
> > >
> > > However, we may still need to define the RISC-V EFI protocol to
> > > support ACPI for other OS (FreeBSD) which doesn't have
> > > a stub like loader that uses DT.
> > >
> > > In that case, where should we document it ? UEFI spec or RISC-V platform spec ?
> >
> > Defining EFI protocols outside the UEFI spec has precedents, e.g. the
> > EFI_TCG2_PROTOCOL is defined in a specification hosted by the Trusted
> > Computing Group.
> >
> 
> The 'E' in EFI means 'extensible' and the UEFI spec was never intended
> as an exhaustive reference of all imaginable protocols. It is
> perfectly fine to define your own protocols, and document them
> wherever appropriate.
> 
> > The UEFI Forum prefers an implemention first approach. We should
> > demonstrate with a patched EDK II or U-Boot and a patched Linux that
> > what we define is working before creating a change request.
> >
> 
> ... if needed. There is no need to incorporate this into the UEFI spec.
> 
> > Let's start with a draft protocol specification on Github and then
> > develop the necessary patches.
> >
> 
> Agreed.

Hi Ard,
   Here is the draft EFI_RISCV_BOOT_PROTOCOL specification.
   https://github.com/riscv-non-isa/riscv-uefi/releases/download/0.3/EFI_RISCV_PROTOCOL-spec.pdf

   If you are fine with this, we can freeze this spec. Thanks a lot for
   your help on this.

Thanks
Sunil
> 
> And to Heinrich's point regarding that there should not be a need for
> this protocol: I completely agree. The fact that passing the
> boot-hartid in a0 is part of the boot protocol is unfortunate, and
> sadly, the EFI stub needs to implement what the boot protocol
> stipulates, even though it is not a great design to begin with.

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Re: Question regarding "boot-hartid" DT node

[Ard Biesheuvel]

> Hi Ard,
>    Here is the draft EFI_RISCV_BOOT_PROTOCOL specification.
>    https://github.com/riscv-non-isa/riscv-uefi/releases/download/0.3/EFI_RISCV_PROTOCOL-spec.pdf
>
>    If you are fine with this, we can freeze this spec. Thanks a lot for
>    your help on this.

Please don't use the EFI_ prefix, it is reserved for protocols that
are defined in the UEFI or PI specifications.

Other than that, this looks fine to me.

-- 
Ard.

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Re: Question regarding "boot-hartid" DT node

[Sunil V L]

On Thu, Jan 13, 2022 at 10:50:11AM +0100, Ard Biesheuvel wrote:
> > Hi Ard,
> >    Here is the draft EFI_RISCV_BOOT_PROTOCOL specification.
> >    https://github.com/riscv-non-isa/riscv-uefi/releases/download/0.3/EFI_RISCV_PROTOCOL-spec.pdf
> >
> >    If you are fine with this, we can freeze this spec. Thanks a lot for
> >    your help on this.
> 
> Please don't use the EFI_ prefix, it is reserved for protocols that
> are defined in the UEFI or PI specifications.

Oh OK. I didn't know that. TCG2 protocols also start with EFI prefix. Is
that a mistake?

Would "RISCV_EFI_BOOT_PROTOCOL" be better?

Thanks
Sunil
> 
> Other than that, this looks fine to me.
> 
> -- 
> Ard.

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Re: Question regarding "boot-hartid" DT node

[Ard Biesheuvel]

On Thu, 13 Jan 2022 at 10:59, Sunil V L <sunilvl@ventanamicro.com> wrote:
>
> On Thu, Jan 13, 2022 at 10:50:11AM +0100, Ard Biesheuvel wrote:
> > > Hi Ard,
> > >    Here is the draft EFI_RISCV_BOOT_PROTOCOL specification.
> > >    https://github.com/riscv-non-isa/riscv-uefi/releases/download/0.3/EFI_RISCV_PROTOCOL-spec.pdf
> > >
> > >    If you are fine with this, we can freeze this spec. Thanks a lot for
> > >    your help on this.
> >
> > Please don't use the EFI_ prefix, it is reserved for protocols that
> > are defined in the UEFI or PI specifications.
>
> Oh OK. I didn't know that. TCG2 protocols also start with EFI prefix. Is
> that a mistake?
>

Yes.

> Would "RISCV_EFI_BOOT_PROTOCOL" be better?
>

Yes, or RISCV_BOOT_PROTOCOL. The EFI is kind of redundant since we are
dealing with a EFI protocol.

> Thanks
> Sunil
> >
> > Other than that, this looks fine to me.
> >
> > --
> > Ard.

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Re: Question regarding "boot-hartid" DT node

[Sunil V L]

On Thu, Jan 13, 2022 at 11:01:10AM +0100, Ard Biesheuvel wrote:
> On Thu, 13 Jan 2022 at 10:59, Sunil V L <sunilvl@ventanamicro.com> wrote:
> >
> > On Thu, Jan 13, 2022 at 10:50:11AM +0100, Ard Biesheuvel wrote:
> > > > Hi Ard,
> > > >    Here is the draft EFI_RISCV_BOOT_PROTOCOL specification.
> > > >    https://github.com/riscv-non-isa/riscv-uefi/releases/download/0.3/EFI_RISCV_PROTOCOL-spec.pdf
> > > >
> > > >    If you are fine with this, we can freeze this spec. Thanks a lot for
> > > >    your help on this.
> > >
> > > Please don't use the EFI_ prefix, it is reserved for protocols that
> > > are defined in the UEFI or PI specifications.
> >
> > Oh OK. I didn't know that. TCG2 protocols also start with EFI prefix. Is
> > that a mistake?
> >
> 
> Yes.
> 
> > Would "RISCV_EFI_BOOT_PROTOCOL" be better?
> >
> 
> Yes, or RISCV_BOOT_PROTOCOL. The EFI is kind of redundant since we are
> dealing with a EFI protocol.
Thanks a lot!, Ard. While I agree EFI is kind of redundant, I still prefer to
keep it. Since RISC-V supports both EFI and non-EFI systems, having EFI
clearly indicates this is for EFI systems.

Thanks
Sunil

> 
> > Thanks
> > Sunil
> > >
> > > Other than that, this looks fine to me.
> > >
> > > --
> > > Ard.

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