[U-Boot] MIPS UHI spec

[U-Boot] MIPS UHI spec

[Matthew Fortune]

Hi Daniel,

The spec for MIPS Unified Hosting Interface is available here:

http://prplfoundation.org/wiki/MIPS_documentation

As we have previously discussed, this is an ideal place to
define the handover of device tree data from bootloader to
kernel. Using a0 == -2 and defining which register(s) you
need for the actual data will fit nicely. I'll happily
include whatever is decided into the next version of the spec.

This is also the spec I would like to use to implement a syscall
interface. Previous post on the topic:

http://lists.denx.de/pipermail/u-boot/2014-December/198007.html

Only a subset of the operations would be implemented for u-boot
and would be strictly limited to sit on top of the functionality
that is already exposed to standalone applications with GPL
exceptions. Some of the operations need a bit of wrapper code
around the API functions i.e. The write operation would only be
handled for FD 1 and 2 and would be implemented as a loop
sending each byte of the buffer via putc.

UHI also provides a semi-hosting solution for u-boot itself
which it could use to obtain files over the EJTAG interface.

Initial implementation of the syscall interface will be posted
relatively soon.

Thanks,
Matthew

[U-Boot] MIPS UHI spec

[Paul Burton]

On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
> Hi Daniel,
> 
> The spec for MIPS Unified Hosting Interface is available here:
> 
> http://prplfoundation.org/wiki/MIPS_documentation
> 
> As we have previously discussed, this is an ideal place to
> define the handover of device tree data from bootloader to
> kernel. Using a0 == -2 and defining which register(s) you
> need for the actual data will fit nicely. I'll happily
> include whatever is decided into the next version of the spec.

(CC +Andrew, Ezequiel, James, James)

On the talk of DT handover, this recent patchset adding support for a
system doing so to Linux is relevant:

    http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html

I'm also working on a system for which I'll need to implement DT
handover very soon. It would be very nice if we could agree on some
standard way of doing so (and eventually if the code on the Linux side
can be generic enough to allow a multiplatform kernel).

Thanks,
    Paul

Re: [U-Boot] MIPS UHI spec

[Daniel Schwierzeck]

2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>> Hi Daniel,
>>
>> The spec for MIPS Unified Hosting Interface is available here:
>>
>> http://prplfoundation.org/wiki/MIPS_documentation
>>
>> As we have previously discussed, this is an ideal place to
>> define the handover of device tree data from bootloader to
>> kernel. Using a0 == -2 and defining which register(s) you
>> need for the actual data will fit nicely. I'll happily
>> include whatever is decided into the next version of the spec.

this originates from an off-list discussion some months ago started by
John Crispin.

(CC +John, Ralf, Jonas, linux-mips)

>
> (CC +Andrew, Ezequiel, James, James)
>
> On the talk of DT handover, this recent patchset adding support for a
> system doing so to Linux is relevant:
>
>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>
> I'm also working on a system for which I'll need to implement DT
> handover very soon. It would be very nice if we could agree on some
> standard way of doing so (and eventually if the code on the Linux side
> can be generic enough to allow a multiplatform kernel).
>

to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
blob. It is a simple extension and should not interfere with the
various legacy boot interfaces.

U-Boot mainline code is almost ready for DT handover. I have prepared
a patch [1] which completes it by implementing my proposal.

[1] http://git.denx.de/?p=u-boot/u-boot-mips.git;a=commitdiff;h=3464e8de491c640d14d72853a741cc367ebabc79

-- 
- Daniel

[U-Boot] MIPS UHI spec

[Daniel Schwierzeck]

2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>> Hi Daniel,
>>
>> The spec for MIPS Unified Hosting Interface is available here:
>>
>> http://prplfoundation.org/wiki/MIPS_documentation
>>
>> As we have previously discussed, this is an ideal place to
>> define the handover of device tree data from bootloader to
>> kernel. Using a0 == -2 and defining which register(s) you
>> need for the actual data will fit nicely. I'll happily
>> include whatever is decided into the next version of the spec.

this originates from an off-list discussion some months ago started by
John Crispin.

(CC +John, Ralf, Jonas, linux-mips)

>
> (CC +Andrew, Ezequiel, James, James)
>
> On the talk of DT handover, this recent patchset adding support for a
> system doing so to Linux is relevant:
>
>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>
> I'm also working on a system for which I'll need to implement DT
> handover very soon. It would be very nice if we could agree on some
> standard way of doing so (and eventually if the code on the Linux side
> can be generic enough to allow a multiplatform kernel).
>

to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
blob. It is a simple extension and should not interfere with the
various legacy boot interfaces.

U-Boot mainline code is almost ready for DT handover. I have prepared
a patch [1] which completes it by implementing my proposal.

[1] http://git.denx.de/?p=u-boot/u-boot-mips.git;a=commitdiff;h=3464e8de491c640d14d72853a741cc367ebabc79

-- 
- Daniel

Re: [U-Boot] MIPS UHI spec

[Andrew Bresticker]

Hi,

On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
<daniel.schwierzeck@gmail.com> wrote:
> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>> Hi Daniel,
>>>
>>> The spec for MIPS Unified Hosting Interface is available here:
>>>
>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>
>>> As we have previously discussed, this is an ideal place to
>>> define the handover of device tree data from bootloader to
>>> kernel. Using a0 == -2 and defining which register(s) you
>>> need for the actual data will fit nicely. I'll happily
>>> include whatever is decided into the next version of the spec.
>
> this originates from an off-list discussion some months ago started by
> John Crispin.
>
> (CC +John, Ralf, Jonas, linux-mips)
>
>>
>> (CC +Andrew, Ezequiel, James, James)
>>
>> On the talk of DT handover, this recent patchset adding support for a
>> system doing so to Linux is relevant:
>>
>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>
>> I'm also working on a system for which I'll need to implement DT
>> handover very soon. It would be very nice if we could agree on some
>> standard way of doing so (and eventually if the code on the Linux side
>> can be generic enough to allow a multiplatform kernel).

+1.  I would like to see this happen as well.

> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> blob. It is a simple extension and should not interfere with the
> various legacy boot interfaces.
>
> U-Boot mainline code is almost ready for DT handover. I have prepared
> a patch [1] which completes it by implementing my proposal.

Hmm... we decided to follow the ARM convention here ($a0 = 0, $a1 =
-1, $a2 = physical address of DTB), which is also what the BMIPS
platform (submitted by Kevin) is using for DT handover.  Is there
already a platform using the protocol you described?  It's still early
enough that we could change the DT handover for Pistachio, but it
would be good to agree on something soon.

Thanks,
Andrew

[U-Boot] MIPS UHI spec

[Andrew Bresticker]

Hi,

On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
<daniel.schwierzeck@gmail.com> wrote:
> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>> Hi Daniel,
>>>
>>> The spec for MIPS Unified Hosting Interface is available here:
>>>
>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>
>>> As we have previously discussed, this is an ideal place to
>>> define the handover of device tree data from bootloader to
>>> kernel. Using a0 == -2 and defining which register(s) you
>>> need for the actual data will fit nicely. I'll happily
>>> include whatever is decided into the next version of the spec.
>
> this originates from an off-list discussion some months ago started by
> John Crispin.
>
> (CC +John, Ralf, Jonas, linux-mips)
>
>>
>> (CC +Andrew, Ezequiel, James, James)
>>
>> On the talk of DT handover, this recent patchset adding support for a
>> system doing so to Linux is relevant:
>>
>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>
>> I'm also working on a system for which I'll need to implement DT
>> handover very soon. It would be very nice if we could agree on some
>> standard way of doing so (and eventually if the code on the Linux side
>> can be generic enough to allow a multiplatform kernel).

+1.  I would like to see this happen as well.

> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> blob. It is a simple extension and should not interfere with the
> various legacy boot interfaces.
>
> U-Boot mainline code is almost ready for DT handover. I have prepared
> a patch [1] which completes it by implementing my proposal.

Hmm... we decided to follow the ARM convention here ($a0 = 0, $a1 =
-1, $a2 = physical address of DTB), which is also what the BMIPS
platform (submitted by Kevin) is using for DT handover.  Is there
already a platform using the protocol you described?  It's still early
enough that we could change the DT handover for Pistachio, but it
would be good to agree on something soon.

Thanks,
Andrew

Re: [U-Boot] MIPS UHI spec

[Daniel Schwierzeck]

2015-02-26 19:23 GMT+01:00 Andrew Bresticker <abrestic@chromium.org>:
> Hi,
>
> On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
> <daniel.schwierzeck@gmail.com> wrote:
>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>>> Hi Daniel,
>>>>
>>>> The spec for MIPS Unified Hosting Interface is available here:
>>>>
>>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>>
>>>> As we have previously discussed, this is an ideal place to
>>>> define the handover of device tree data from bootloader to
>>>> kernel. Using a0 == -2 and defining which register(s) you
>>>> need for the actual data will fit nicely. I'll happily
>>>> include whatever is decided into the next version of the spec.
>>
>> this originates from an off-list discussion some months ago started by
>> John Crispin.
>>
>> (CC +John, Ralf, Jonas, linux-mips)
>>
>>>
>>> (CC +Andrew, Ezequiel, James, James)
>>>
>>> On the talk of DT handover, this recent patchset adding support for a
>>> system doing so to Linux is relevant:
>>>
>>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>>
>>> I'm also working on a system for which I'll need to implement DT
>>> handover very soon. It would be very nice if we could agree on some
>>> standard way of doing so (and eventually if the code on the Linux side
>>> can be generic enough to allow a multiplatform kernel).
>
> +1.  I would like to see this happen as well.
>
>> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>> blob. It is a simple extension and should not interfere with the
>> various legacy boot interfaces.
>>
>> U-Boot mainline code is almost ready for DT handover. I have prepared
>> a patch [1] which completes it by implementing my proposal.
>
> Hmm... we decided to follow the ARM convention here ($a0 = 0, $a1 =
> -1, $a2 = physical address of DTB), which is also what the BMIPS
> platform (submitted by Kevin) is using for DT handover.  Is there
> already a platform using the protocol you described?

no, but with its publication the MIPS UHI spec is kind of official.
AFAIK patches to support UHI in gcc, gdb, U-Boot etc. are already
submitted or prepared. Matthew suggested that new boot protocols
should be compliant with UHI. I think the ARM convention does not fit
to UHI.

> It's still early
> enough that we could change the DT handover for Pistachio, but it
> would be good to agree on something soon.
>
> Thanks,
> Andrew

-- 
- Daniel

[U-Boot] MIPS UHI spec

[Daniel Schwierzeck]

2015-02-26 19:23 GMT+01:00 Andrew Bresticker <abrestic@chromium.org>:
> Hi,
>
> On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
> <daniel.schwierzeck@gmail.com> wrote:
>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>>> Hi Daniel,
>>>>
>>>> The spec for MIPS Unified Hosting Interface is available here:
>>>>
>>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>>
>>>> As we have previously discussed, this is an ideal place to
>>>> define the handover of device tree data from bootloader to
>>>> kernel. Using a0 == -2 and defining which register(s) you
>>>> need for the actual data will fit nicely. I'll happily
>>>> include whatever is decided into the next version of the spec.
>>
>> this originates from an off-list discussion some months ago started by
>> John Crispin.
>>
>> (CC +John, Ralf, Jonas, linux-mips)
>>
>>>
>>> (CC +Andrew, Ezequiel, James, James)
>>>
>>> On the talk of DT handover, this recent patchset adding support for a
>>> system doing so to Linux is relevant:
>>>
>>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>>
>>> I'm also working on a system for which I'll need to implement DT
>>> handover very soon. It would be very nice if we could agree on some
>>> standard way of doing so (and eventually if the code on the Linux side
>>> can be generic enough to allow a multiplatform kernel).
>
> +1.  I would like to see this happen as well.
>
>> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>> blob. It is a simple extension and should not interfere with the
>> various legacy boot interfaces.
>>
>> U-Boot mainline code is almost ready for DT handover. I have prepared
>> a patch [1] which completes it by implementing my proposal.
>
> Hmm... we decided to follow the ARM convention here ($a0 = 0, $a1 =
> -1, $a2 = physical address of DTB), which is also what the BMIPS
> platform (submitted by Kevin) is using for DT handover.  Is there
> already a platform using the protocol you described?

no, but with its publication the MIPS UHI spec is kind of official.
AFAIK patches to support UHI in gcc, gdb, U-Boot etc. are already
submitted or prepared. Matthew suggested that new boot protocols
should be compliant with UHI. I think the ARM convention does not fit
to UHI.

> It's still early
> enough that we could change the DT handover for Pistachio, but it
> would be good to agree on something soon.
>
> Thanks,
> Andrew

-- 
- Daniel

Re: [U-Boot] MIPS UHI spec

[Andrew Bresticker]

On Fri, Feb 27, 2015 at 2:44 AM, Daniel Schwierzeck
<daniel.schwierzeck@gmail.com> wrote:
> 2015-02-26 19:23 GMT+01:00 Andrew Bresticker <abrestic@chromium.org>:
>> Hi,
>>
>> On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
>> <daniel.schwierzeck@gmail.com> wrote:
>>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>>>> Hi Daniel,
>>>>>
>>>>> The spec for MIPS Unified Hosting Interface is available here:
>>>>>
>>>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>>>
>>>>> As we have previously discussed, this is an ideal place to
>>>>> define the handover of device tree data from bootloader to
>>>>> kernel. Using a0 == -2 and defining which register(s) you
>>>>> need for the actual data will fit nicely. I'll happily
>>>>> include whatever is decided into the next version of the spec.
>>>
>>> this originates from an off-list discussion some months ago started by
>>> John Crispin.
>>>
>>> (CC +John, Ralf, Jonas, linux-mips)
>>>
>>>>
>>>> (CC +Andrew, Ezequiel, James, James)
>>>>
>>>> On the talk of DT handover, this recent patchset adding support for a
>>>> system doing so to Linux is relevant:
>>>>
>>>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>>>
>>>> I'm also working on a system for which I'll need to implement DT
>>>> handover very soon. It would be very nice if we could agree on some
>>>> standard way of doing so (and eventually if the code on the Linux side
>>>> can be generic enough to allow a multiplatform kernel).
>>
>> +1.  I would like to see this happen as well.
>>
>>> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>>> blob. It is a simple extension and should not interfere with the
>>> various legacy boot interfaces.
>>>
>>> U-Boot mainline code is almost ready for DT handover. I have prepared
>>> a patch [1] which completes it by implementing my proposal.
>>
>> Hmm... we decided to follow the ARM convention here ($a0 = 0, $a1 =
>> -1, $a2 = physical address of DTB), which is also what the BMIPS
>> platform (submitted by Kevin) is using for DT handover.  Is there
>> already a platform using the protocol you described?
>
> no, but with its publication the MIPS UHI spec is kind of official.
> AFAIK patches to support UHI in gcc, gdb, U-Boot etc. are already
> submitted or prepared. Matthew suggested that new boot protocols
> should be compliant with UHI. I think the ARM convention does not fit
> to UHI.

Ok, I think we can change the boot protocol on Pistachio to match UHI then.

-Andrew

[U-Boot] MIPS UHI spec

[Andrew Bresticker]

On Fri, Feb 27, 2015 at 2:44 AM, Daniel Schwierzeck
<daniel.schwierzeck@gmail.com> wrote:
> 2015-02-26 19:23 GMT+01:00 Andrew Bresticker <abrestic@chromium.org>:
>> Hi,
>>
>> On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
>> <daniel.schwierzeck@gmail.com> wrote:
>>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>>>> Hi Daniel,
>>>>>
>>>>> The spec for MIPS Unified Hosting Interface is available here:
>>>>>
>>>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>>>
>>>>> As we have previously discussed, this is an ideal place to
>>>>> define the handover of device tree data from bootloader to
>>>>> kernel. Using a0 == -2 and defining which register(s) you
>>>>> need for the actual data will fit nicely. I'll happily
>>>>> include whatever is decided into the next version of the spec.
>>>
>>> this originates from an off-list discussion some months ago started by
>>> John Crispin.
>>>
>>> (CC +John, Ralf, Jonas, linux-mips)
>>>
>>>>
>>>> (CC +Andrew, Ezequiel, James, James)
>>>>
>>>> On the talk of DT handover, this recent patchset adding support for a
>>>> system doing so to Linux is relevant:
>>>>
>>>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>>>
>>>> I'm also working on a system for which I'll need to implement DT
>>>> handover very soon. It would be very nice if we could agree on some
>>>> standard way of doing so (and eventually if the code on the Linux side
>>>> can be generic enough to allow a multiplatform kernel).
>>
>> +1.  I would like to see this happen as well.
>>
>>> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>>> blob. It is a simple extension and should not interfere with the
>>> various legacy boot interfaces.
>>>
>>> U-Boot mainline code is almost ready for DT handover. I have prepared
>>> a patch [1] which completes it by implementing my proposal.
>>
>> Hmm... we decided to follow the ARM convention here ($a0 = 0, $a1 =
>> -1, $a2 = physical address of DTB), which is also what the BMIPS
>> platform (submitted by Kevin) is using for DT handover.  Is there
>> already a platform using the protocol you described?
>
> no, but with its publication the MIPS UHI spec is kind of official.
> AFAIK patches to support UHI in gcc, gdb, U-Boot etc. are already
> submitted or prepared. Matthew suggested that new boot protocols
> should be compliant with UHI. I think the ARM convention does not fit
> to UHI.

Ok, I think we can change the boot protocol on Pistachio to match UHI then.

-Andrew

RE: [U-Boot] MIPS UHI spec

[Matthew Fortune]

Andrew Bresticker <abrestic@chromium.org> writes:
> On Fri, Feb 27, 2015 at 2:44 AM, Daniel Schwierzeck
> <daniel.schwierzeck@gmail.com> wrote:
> > 2015-02-26 19:23 GMT+01:00 Andrew Bresticker <abrestic@chromium.org>:
> >> Hi,
> >>
> >> On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
> >> <daniel.schwierzeck@gmail.com> wrote:
> >>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
> >>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
> >>>>> Hi Daniel,
> >>>>>
> >>>>> The spec for MIPS Unified Hosting Interface is available here:
> >>>>>
> >>>>> http://prplfoundation.org/wiki/MIPS_documentation
> >>>>>
> >>>>> As we have previously discussed, this is an ideal place to define
> >>>>> the handover of device tree data from bootloader to kernel. Using
> >>>>> a0 == -2 and defining which register(s) you need for the actual
> >>>>> data will fit nicely. I'll happily include whatever is decided
> >>>>> into the next version of the spec.
> >>>
> >>> this originates from an off-list discussion some months ago started
> >>> by John Crispin.
> >>>
> >>> (CC +John, Ralf, Jonas, linux-mips)
> >>>
> >>>>
> >>>> (CC +Andrew, Ezequiel, James, James)
> >>>>
> >>>> On the talk of DT handover, this recent patchset adding support for
> >>>> a system doing so to Linux is relevant:
> >>>>
> >>>>
> >>>> http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
> >>>>
> >>>> I'm also working on a system for which I'll need to implement DT
> >>>> handover very soon. It would be very nice if we could agree on some
> >>>> standard way of doing so (and eventually if the code on the Linux
> >>>> side can be generic enough to allow a multiplatform kernel).
> >>
> >> +1.  I would like to see this happen as well.
> >>
> >>> to be conformant with UHI I propose $a0 == -2 and $a1 == address of
> >>> DT blob. It is a simple extension and should not interfere with the
> >>> various legacy boot interfaces.
> >>>
> >>> U-Boot mainline code is almost ready for DT handover. I have
> >>> prepared a patch [1] which completes it by implementing my proposal.
> >>
> >> Hmm... we decided to follow the ARM convention here ($a0 = 0, $a1 =
> >> -1, $a2 = physical address of DTB), which is also what the BMIPS
> >> platform (submitted by Kevin) is using for DT handover.  Is there
> >> already a platform using the protocol you described?
> >
> > no, but with its publication the MIPS UHI spec is kind of official.
> > AFAIK patches to support UHI in gcc, gdb, U-Boot etc. are already
> > submitted or prepared. Matthew suggested that new boot protocols
> > should be compliant with UHI. I think the ARM convention does not fit
> > to UHI.
> 
> Ok, I think we can change the boot protocol on Pistachio to match UHI
> then.

If that is possible then it would be good. The UHI spec is intended to
involve the various communities in further changes but the initial version
had to make some tradeoffs and define some rules.

FWIW I was trying to keep the overall control of the handover protocol
ultra simple by having a0 dictate the meaning of all other registers.
The ARM protocol has ended up with two registers to indicate DTB handover
making the a0==0 case have sub-categories.

Let me know if this doesn't end up possible and we can figure out how to
cope with that in the spec.

thanks,
Matthew

RE: [U-Boot] MIPS UHI spec

[James Hartley]

Hi Matthew,

> -----Original Message-----
> From: Matthew Fortune
> Sent: 27 February 2015 20:46
> To: Andrew Bresticker; Daniel Schwierzeck
> Cc: Paul Burton; u-boot@lists.denx.de; Ezequiel Garcia; James Hartley;
> James Hogan; John Crispin; Jonas Gorski; Ralf Baechle; Linux-MIPS;
> cernekee@chromium.org
> Subject: RE: [U-Boot] MIPS UHI spec
> 
> Andrew Bresticker <abrestic@chromium.org> writes:
> > On Fri, Feb 27, 2015 at 2:44 AM, Daniel Schwierzeck
> > <daniel.schwierzeck@gmail.com> wrote:
> > > 2015-02-26 19:23 GMT+01:00 Andrew Bresticker
> <abrestic@chromium.org>:
> > >> Hi,
> > >>
> > >> On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
> > >> <daniel.schwierzeck@gmail.com> wrote:
> > >>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
> > >>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
> > >>>>> Hi Daniel,
> > >>>>>
> > >>>>> The spec for MIPS Unified Hosting Interface is available here:
> > >>>>>
> > >>>>> http://prplfoundation.org/wiki/MIPS_documentation
> > >>>>>
> > >>>>> As we have previously discussed, this is an ideal place to
> > >>>>> define the handover of device tree data from bootloader to
> > >>>>> kernel. Using
> > >>>>> a0 == -2 and defining which register(s) you need for the actual
> > >>>>> data will fit nicely. I'll happily include whatever is decided
> > >>>>> into the next version of the spec.
> > >>>
> > >>> this originates from an off-list discussion some months ago
> > >>> started by John Crispin.
> > >>>
> > >>> (CC +John, Ralf, Jonas, linux-mips)
> > >>>
> > >>>>
> > >>>> (CC +Andrew, Ezequiel, James, James)
> > >>>>
> > >>>> On the talk of DT handover, this recent patchset adding support
> > >>>> for a system doing so to Linux is relevant:
> > >>>>
> > >>>>
> > >>>> http://www.linux-mips.org/archives/linux-mips/2015-
> 02/msg00312.ht
> > >>>> ml
> > >>>>
> > >>>> I'm also working on a system for which I'll need to implement DT
> > >>>> handover very soon. It would be very nice if we could agree on
> > >>>> some standard way of doing so (and eventually if the code on the
> > >>>> Linux side can be generic enough to allow a multiplatform kernel).
> > >>
> > >> +1.  I would like to see this happen as well.
> > >>
> > >>> to be conformant with UHI I propose $a0 == -2 and $a1 == address
> > >>> of DT blob. It is a simple extension and should not interfere with
> > >>> the various legacy boot interfaces.
> > >>>
> > >>> U-Boot mainline code is almost ready for DT handover. I have
> > >>> prepared a patch [1] which completes it by implementing my proposal.
> > >>
> > >> Hmm... we decided to follow the ARM convention here ($a0 = 0, $a1 =
> > >> -1, $a2 = physical address of DTB), which is also what the BMIPS
> > >> platform (submitted by Kevin) is using for DT handover.  Is there
> > >> already a platform using the protocol you described?
> > >
> > > no, but with its publication the MIPS UHI spec is kind of official.
> > > AFAIK patches to support UHI in gcc, gdb, U-Boot etc. are already
> > > submitted or prepared. Matthew suggested that new boot protocols
> > > should be compliant with UHI. I think the ARM convention does not
> > > fit to UHI.
> >
> > Ok, I think we can change the boot protocol on Pistachio to match UHI
> > then.
> 
> If that is possible then it would be good. The UHI spec is intended to involve
> the various communities in further changes but the initial version had to
> make some tradeoffs and define some rules.
> 
> FWIW I was trying to keep the overall control of the handover protocol ultra
> simple by having a0 dictate the meaning of all other registers.
> The ARM protocol has ended up with two registers to indicate DTB handover
> making the a0==0 case have sub-categories.
> 
> Let me know if this doesn't end up possible and we can figure out how to
> cope with that in the spec.

FYI: We've updated Pistachio to use: $a0 == -2 and $a1 == address of DT blob.
This will filter up into a V2 of the patches submitted upstream.

Thanks,
James.

Re: [U-Boot] MIPS UHI spec

[Andrew Bresticker]

Hi Daniel,

On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
<daniel.schwierzeck@gmail.com> wrote:
> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>> Hi Daniel,
>>>
>>> The spec for MIPS Unified Hosting Interface is available here:
>>>
>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>
>>> As we have previously discussed, this is an ideal place to
>>> define the handover of device tree data from bootloader to
>>> kernel. Using a0 == -2 and defining which register(s) you
>>> need for the actual data will fit nicely. I'll happily
>>> include whatever is decided into the next version of the spec.
>
> this originates from an off-list discussion some months ago started by
> John Crispin.
>
> (CC +John, Ralf, Jonas, linux-mips)
>
>>
>> (CC +Andrew, Ezequiel, James, James)
>>
>> On the talk of DT handover, this recent patchset adding support for a
>> system doing so to Linux is relevant:
>>
>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>
>> I'm also working on a system for which I'll need to implement DT
>> handover very soon. It would be very nice if we could agree on some
>> standard way of doing so (and eventually if the code on the Linux side
>> can be generic enough to allow a multiplatform kernel).
>>
>
> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> blob. It is a simple extension and should not interfere with the
> various legacy boot interfaces.

Just to be clear, is $a1 expected to be the physical or virtual
(KSEG0) address of the DTB?

Thanks,
Andrew

[U-Boot] MIPS UHI spec

[Andrew Bresticker]

Hi Daniel,

On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
<daniel.schwierzeck@gmail.com> wrote:
> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>> Hi Daniel,
>>>
>>> The spec for MIPS Unified Hosting Interface is available here:
>>>
>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>
>>> As we have previously discussed, this is an ideal place to
>>> define the handover of device tree data from bootloader to
>>> kernel. Using a0 == -2 and defining which register(s) you
>>> need for the actual data will fit nicely. I'll happily
>>> include whatever is decided into the next version of the spec.
>
> this originates from an off-list discussion some months ago started by
> John Crispin.
>
> (CC +John, Ralf, Jonas, linux-mips)
>
>>
>> (CC +Andrew, Ezequiel, James, James)
>>
>> On the talk of DT handover, this recent patchset adding support for a
>> system doing so to Linux is relevant:
>>
>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>
>> I'm also working on a system for which I'll need to implement DT
>> handover very soon. It would be very nice if we could agree on some
>> standard way of doing so (and eventually if the code on the Linux side
>> can be generic enough to allow a multiplatform kernel).
>>
>
> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> blob. It is a simple extension and should not interfere with the
> various legacy boot interfaces.

Just to be clear, is $a1 expected to be the physical or virtual
(KSEG0) address of the DTB?

Thanks,
Andrew

Re: [U-Boot] MIPS UHI spec

[Daniel Schwierzeck]

Am 09.03.2015 um 18:04 schrieb Andrew Bresticker:
> Hi Daniel,
> 
> On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
> <daniel.schwierzeck@gmail.com> wrote:
>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>>> Hi Daniel,
>>>>
>>>> The spec for MIPS Unified Hosting Interface is available here:
>>>>
>>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>>
>>>> As we have previously discussed, this is an ideal place to
>>>> define the handover of device tree data from bootloader to
>>>> kernel. Using a0 == -2 and defining which register(s) you
>>>> need for the actual data will fit nicely. I'll happily
>>>> include whatever is decided into the next version of the spec.
>>
>> this originates from an off-list discussion some months ago started by
>> John Crispin.
>>
>> (CC +John, Ralf, Jonas, linux-mips)
>>
>>>
>>> (CC +Andrew, Ezequiel, James, James)
>>>
>>> On the talk of DT handover, this recent patchset adding support for a
>>> system doing so to Linux is relevant:
>>>
>>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>>
>>> I'm also working on a system for which I'll need to implement DT
>>> handover very soon. It would be very nice if we could agree on some
>>> standard way of doing so (and eventually if the code on the Linux side
>>> can be generic enough to allow a multiplatform kernel).
>>>
>>
>> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>> blob. It is a simple extension and should not interfere with the
>> various legacy boot interfaces.
> 
> Just to be clear, is $a1 expected to be the physical or virtual
> (KSEG0) address of the DTB?
> 

U-Boot currently uses KSEG0 addresses for kernel entry and initramfs.
Therefore the DTB address would be also KSEG0. But I'm not sure if it is
correct for MIPS64. Shouldn't the kernel sanitize the DTB address anyway
like it's done with initramfs? Maybe Matthew or others could comment.

-- 
- Daniel

[U-Boot] MIPS UHI spec

[Daniel Schwierzeck]

Am 09.03.2015 um 18:04 schrieb Andrew Bresticker:
> Hi Daniel,
> 
> On Thu, Feb 26, 2015 at 4:37 AM, Daniel Schwierzeck
> <daniel.schwierzeck@gmail.com> wrote:
>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>>> Hi Daniel,
>>>>
>>>> The spec for MIPS Unified Hosting Interface is available here:
>>>>
>>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>>
>>>> As we have previously discussed, this is an ideal place to
>>>> define the handover of device tree data from bootloader to
>>>> kernel. Using a0 == -2 and defining which register(s) you
>>>> need for the actual data will fit nicely. I'll happily
>>>> include whatever is decided into the next version of the spec.
>>
>> this originates from an off-list discussion some months ago started by
>> John Crispin.
>>
>> (CC +John, Ralf, Jonas, linux-mips)
>>
>>>
>>> (CC +Andrew, Ezequiel, James, James)
>>>
>>> On the talk of DT handover, this recent patchset adding support for a
>>> system doing so to Linux is relevant:
>>>
>>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>>
>>> I'm also working on a system for which I'll need to implement DT
>>> handover very soon. It would be very nice if we could agree on some
>>> standard way of doing so (and eventually if the code on the Linux side
>>> can be generic enough to allow a multiplatform kernel).
>>>
>>
>> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>> blob. It is a simple extension and should not interfere with the
>> various legacy boot interfaces.
> 
> Just to be clear, is $a1 expected to be the physical or virtual
> (KSEG0) address of the DTB?
> 

U-Boot currently uses KSEG0 addresses for kernel entry and initramfs.
Therefore the DTB address would be also KSEG0. But I'm not sure if it is
correct for MIPS64. Shouldn't the kernel sanitize the DTB address anyway
like it's done with initramfs? Maybe Matthew or others could comment.

-- 
- Daniel

Re: [U-Boot] MIPS UHI spec

[James Hogan]

[-- Attachment #1: Type: text/plain, Size: 2166 bytes --]

On 26/02/15 12:37, Daniel Schwierzeck wrote:
> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>> Hi Daniel,
>>>
>>> The spec for MIPS Unified Hosting Interface is available here:
>>>
>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>
>>> As we have previously discussed, this is an ideal place to
>>> define the handover of device tree data from bootloader to
>>> kernel. Using a0 == -2 and defining which register(s) you
>>> need for the actual data will fit nicely. I'll happily
>>> include whatever is decided into the next version of the spec.
> 
> this originates from an off-list discussion some months ago started by
> John Crispin.
> 
> (CC +John, Ralf, Jonas, linux-mips)
> 
>>
>> (CC +Andrew, Ezequiel, James, James)
>>
>> On the talk of DT handover, this recent patchset adding support for a
>> system doing so to Linux is relevant:
>>
>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>
>> I'm also working on a system for which I'll need to implement DT
>> handover very soon. It would be very nice if we could agree on some
>> standard way of doing so (and eventually if the code on the Linux side
>> can be generic enough to allow a multiplatform kernel).
>>
> 
> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> blob. It is a simple extension and should not interfere with the
> various legacy boot interfaces.

I was just looking at Andrew's patch:
http://patchwork.linux-mips.org/patch/9549/

How would the other registers (i.e. $a2 and $a3) be defined for this
boot interface? I'm guessing any future extensions are envisioned to use
a different negative value of $a0, in which case treating them as
unused/undefined is fine, but perhaps that should be spelt out in the
UHI spec?

Cheers
James

> 
> U-Boot mainline code is almost ready for DT handover. I have prepared
> a patch [1] which completes it by implementing my proposal.
> 
> [1] http://git.denx.de/?p=u-boot/u-boot-mips.git;a=commitdiff;h=3464e8de491c640d14d72853a741cc367ebabc79
> 


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Re: [U-Boot] MIPS UHI spec

[James Hogan]

[-- Attachment #1: Type: text/plain, Size: 2166 bytes --]

On 26/02/15 12:37, Daniel Schwierzeck wrote:
> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>> Hi Daniel,
>>>
>>> The spec for MIPS Unified Hosting Interface is available here:
>>>
>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>
>>> As we have previously discussed, this is an ideal place to
>>> define the handover of device tree data from bootloader to
>>> kernel. Using a0 == -2 and defining which register(s) you
>>> need for the actual data will fit nicely. I'll happily
>>> include whatever is decided into the next version of the spec.
> 
> this originates from an off-list discussion some months ago started by
> John Crispin.
> 
> (CC +John, Ralf, Jonas, linux-mips)
> 
>>
>> (CC +Andrew, Ezequiel, James, James)
>>
>> On the talk of DT handover, this recent patchset adding support for a
>> system doing so to Linux is relevant:
>>
>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>
>> I'm also working on a system for which I'll need to implement DT
>> handover very soon. It would be very nice if we could agree on some
>> standard way of doing so (and eventually if the code on the Linux side
>> can be generic enough to allow a multiplatform kernel).
>>
> 
> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> blob. It is a simple extension and should not interfere with the
> various legacy boot interfaces.

I was just looking at Andrew's patch:
http://patchwork.linux-mips.org/patch/9549/

How would the other registers (i.e. $a2 and $a3) be defined for this
boot interface? I'm guessing any future extensions are envisioned to use
a different negative value of $a0, in which case treating them as
unused/undefined is fine, but perhaps that should be spelt out in the
UHI spec?

Cheers
James

> 
> U-Boot mainline code is almost ready for DT handover. I have prepared
> a patch [1] which completes it by implementing my proposal.
> 
> [1] http://git.denx.de/?p=u-boot/u-boot-mips.git;a=commitdiff;h=3464e8de491c640d14d72853a741cc367ebabc79
> 


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[U-Boot] MIPS UHI spec

[James Hogan]

On 26/02/15 12:37, Daniel Schwierzeck wrote:
> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>> Hi Daniel,
>>>
>>> The spec for MIPS Unified Hosting Interface is available here:
>>>
>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>
>>> As we have previously discussed, this is an ideal place to
>>> define the handover of device tree data from bootloader to
>>> kernel. Using a0 == -2 and defining which register(s) you
>>> need for the actual data will fit nicely. I'll happily
>>> include whatever is decided into the next version of the spec.
> 
> this originates from an off-list discussion some months ago started by
> John Crispin.
> 
> (CC +John, Ralf, Jonas, linux-mips)
> 
>>
>> (CC +Andrew, Ezequiel, James, James)
>>
>> On the talk of DT handover, this recent patchset adding support for a
>> system doing so to Linux is relevant:
>>
>>     http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>
>> I'm also working on a system for which I'll need to implement DT
>> handover very soon. It would be very nice if we could agree on some
>> standard way of doing so (and eventually if the code on the Linux side
>> can be generic enough to allow a multiplatform kernel).
>>
> 
> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> blob. It is a simple extension and should not interfere with the
> various legacy boot interfaces.

I was just looking at Andrew's patch:
http://patchwork.linux-mips.org/patch/9549/

How would the other registers (i.e. $a2 and $a3) be defined for this
boot interface? I'm guessing any future extensions are envisioned to use
a different negative value of $a0, in which case treating them as
unused/undefined is fine, but perhaps that should be spelt out in the
UHI spec?

Cheers
James

> 
> U-Boot mainline code is almost ready for DT handover. I have prepared
> a patch [1] which completes it by implementing my proposal.
> 
> [1] http://git.denx.de/?p=u-boot/u-boot-mips.git;a=commitdiff;h=3464e8de491c640d14d72853a741cc367ebabc79
> 

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RE: [U-Boot] MIPS UHI spec

[Matthew Fortune]

James Hogan <James.Hogan@imgtec.com> writes:
> On 26/02/15 12:37, Daniel Schwierzeck wrote:
> > 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
> >> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
> >>> Hi Daniel,
> >>>
> >>> The spec for MIPS Unified Hosting Interface is available here:
> >>>
> >>> http://prplfoundation.org/wiki/MIPS_documentation
> >>>
> >>> As we have previously discussed, this is an ideal place to define
> >>> the handover of device tree data from bootloader to kernel. Using a0
> >>> == -2 and defining which register(s) you need for the actual data
> >>> will fit nicely. I'll happily include whatever is decided into the
> >>> next version of the spec.
> >
> > this originates from an off-list discussion some months ago started by
> > John Crispin.
> >
> > (CC +John, Ralf, Jonas, linux-mips)
> >
> >>
> >> (CC +Andrew, Ezequiel, James, James)
> >>
> >> On the talk of DT handover, this recent patchset adding support for a
> >> system doing so to Linux is relevant:
> >>
> >>
> >> http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
> >>
> >> I'm also working on a system for which I'll need to implement DT
> >> handover very soon. It would be very nice if we could agree on some
> >> standard way of doing so (and eventually if the code on the Linux
> >> side can be generic enough to allow a multiplatform kernel).
> >>
> >
> > to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> > blob. It is a simple extension and should not interfere with the
> > various legacy boot interfaces.
> 
> I was just looking at Andrew's patch:
> http://patchwork.linux-mips.org/patch/9549/
> 
> How would the other registers (i.e. $a2 and $a3) be defined for this
> boot interface? I'm guessing any future extensions are envisioned to use
> a different negative value of $a0, in which case treating them as
> unused/undefined is fine, but perhaps that should be spelt out in the
> UHI spec?

Sounds sensible. Making it explicit may help prevent anyone extending this
and presuming that they can give meaning to one of the unused registers.

Did anyone come to a conclusion on physical vs virtual address for the
DTB? I forgot to reply to the thread, I would have thought the KSEG0
address would be the obvious choice so that it is immediately usable from
ordinary memory accesses. However, that is only because I don't follow how
the kernel would benefit from being given a physical address. It can't be
remapped except for the case of segmentation control (I believe) so there
seems little risk in using KSEG0.

Thanks,
Matthew

[U-Boot] MIPS UHI spec

[Matthew Fortune]

James Hogan <James.Hogan@imgtec.com> writes:
> On 26/02/15 12:37, Daniel Schwierzeck wrote:
> > 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
> >> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
> >>> Hi Daniel,
> >>>
> >>> The spec for MIPS Unified Hosting Interface is available here:
> >>>
> >>> http://prplfoundation.org/wiki/MIPS_documentation
> >>>
> >>> As we have previously discussed, this is an ideal place to define
> >>> the handover of device tree data from bootloader to kernel. Using a0
> >>> == -2 and defining which register(s) you need for the actual data
> >>> will fit nicely. I'll happily include whatever is decided into the
> >>> next version of the spec.
> >
> > this originates from an off-list discussion some months ago started by
> > John Crispin.
> >
> > (CC +John, Ralf, Jonas, linux-mips)
> >
> >>
> >> (CC +Andrew, Ezequiel, James, James)
> >>
> >> On the talk of DT handover, this recent patchset adding support for a
> >> system doing so to Linux is relevant:
> >>
> >>
> >> http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
> >>
> >> I'm also working on a system for which I'll need to implement DT
> >> handover very soon. It would be very nice if we could agree on some
> >> standard way of doing so (and eventually if the code on the Linux
> >> side can be generic enough to allow a multiplatform kernel).
> >>
> >
> > to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
> > blob. It is a simple extension and should not interfere with the
> > various legacy boot interfaces.
> 
> I was just looking at Andrew's patch:
> http://patchwork.linux-mips.org/patch/9549/
> 
> How would the other registers (i.e. $a2 and $a3) be defined for this
> boot interface? I'm guessing any future extensions are envisioned to use
> a different negative value of $a0, in which case treating them as
> unused/undefined is fine, but perhaps that should be spelt out in the
> UHI spec?

Sounds sensible. Making it explicit may help prevent anyone extending this
and presuming that they can give meaning to one of the unused registers.

Did anyone come to a conclusion on physical vs virtual address for the
DTB? I forgot to reply to the thread, I would have thought the KSEG0
address would be the obvious choice so that it is immediately usable from
ordinary memory accesses. However, that is only because I don't follow how
the kernel would benefit from being given a physical address. It can't be
remapped except for the case of segmentation control (I believe) so there
seems little risk in using KSEG0.

Thanks,
Matthew

Re: [U-Boot] MIPS UHI spec

[James Hogan]

[-- Attachment #1: Type: text/plain, Size: 3669 bytes --]

On 16/03/15 11:53, Matthew Fortune wrote:
> James Hogan <James.Hogan@imgtec.com> writes:
>> On 26/02/15 12:37, Daniel Schwierzeck wrote:
>>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>>>> Hi Daniel,
>>>>>
>>>>> The spec for MIPS Unified Hosting Interface is available here:
>>>>>
>>>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>>>
>>>>> As we have previously discussed, this is an ideal place to define
>>>>> the handover of device tree data from bootloader to kernel. Using a0
>>>>> == -2 and defining which register(s) you need for the actual data
>>>>> will fit nicely. I'll happily include whatever is decided into the
>>>>> next version of the spec.
>>>
>>> this originates from an off-list discussion some months ago started by
>>> John Crispin.
>>>
>>> (CC +John, Ralf, Jonas, linux-mips)
>>>
>>>>
>>>> (CC +Andrew, Ezequiel, James, James)
>>>>
>>>> On the talk of DT handover, this recent patchset adding support for a
>>>> system doing so to Linux is relevant:
>>>>
>>>>
>>>> http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>>>
>>>> I'm also working on a system for which I'll need to implement DT
>>>> handover very soon. It would be very nice if we could agree on some
>>>> standard way of doing so (and eventually if the code on the Linux
>>>> side can be generic enough to allow a multiplatform kernel).
>>>>
>>>
>>> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>>> blob. It is a simple extension and should not interfere with the
>>> various legacy boot interfaces.
>>
>> I was just looking at Andrew's patch:
>> http://patchwork.linux-mips.org/patch/9549/
>>
>> How would the other registers (i.e. $a2 and $a3) be defined for this
>> boot interface? I'm guessing any future extensions are envisioned to use
>> a different negative value of $a0, in which case treating them as
>> unused/undefined is fine, but perhaps that should be spelt out in the
>> UHI spec?
> 
> Sounds sensible. Making it explicit may help prevent anyone extending this
> and presuming that they can give meaning to one of the unused registers.
> 
> Did anyone come to a conclusion on physical vs virtual address for the
> DTB? I forgot to reply to the thread, I would have thought the KSEG0
> address would be the obvious choice so that it is immediately usable from
> ordinary memory accesses. However, that is only because I don't follow how
> the kernel would benefit from being given a physical address. It can't be
> remapped except for the case of segmentation control (I believe) so there
> seems little risk in using KSEG0.

The only obvious cases of physical addresses being passed into MIPS
Linux I can find by grepping for fw_arg[0123] are:
bcm3384: for DT boot, expects physical address of dtb in arg2
fw/sni and lantiq: expect physical arg pointer in arg1.

Physical addresses are probably of more use for arches where only
virtual addresses can be accessed after the MMU is turned on, and Linux
is started with the MMU turned off.

I suppose the problems with using virtual addresses for MIPS would be:
* limits it to low 256MB of RAM usually accessible in kseg0 and kseg1
* as you say, slightly less resistant to segmentation changes

I don't think either of those are really significant problems, though I
can see the appeal of physical addresses for this sort of interface. If
however the rest of the UHI boot APIs deal with directly usable
pointers, then maybe its best to stick with that pattern for consistency.

Cheers
James


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[U-Boot] MIPS UHI spec

[James Hogan]

On 16/03/15 11:53, Matthew Fortune wrote:
> James Hogan <James.Hogan@imgtec.com> writes:
>> On 26/02/15 12:37, Daniel Schwierzeck wrote:
>>> 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>>>> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>>>>> Hi Daniel,
>>>>>
>>>>> The spec for MIPS Unified Hosting Interface is available here:
>>>>>
>>>>> http://prplfoundation.org/wiki/MIPS_documentation
>>>>>
>>>>> As we have previously discussed, this is an ideal place to define
>>>>> the handover of device tree data from bootloader to kernel. Using a0
>>>>> == -2 and defining which register(s) you need for the actual data
>>>>> will fit nicely. I'll happily include whatever is decided into the
>>>>> next version of the spec.
>>>
>>> this originates from an off-list discussion some months ago started by
>>> John Crispin.
>>>
>>> (CC +John, Ralf, Jonas, linux-mips)
>>>
>>>>
>>>> (CC +Andrew, Ezequiel, James, James)
>>>>
>>>> On the talk of DT handover, this recent patchset adding support for a
>>>> system doing so to Linux is relevant:
>>>>
>>>>
>>>> http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>>>>
>>>> I'm also working on a system for which I'll need to implement DT
>>>> handover very soon. It would be very nice if we could agree on some
>>>> standard way of doing so (and eventually if the code on the Linux
>>>> side can be generic enough to allow a multiplatform kernel).
>>>>
>>>
>>> to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>>> blob. It is a simple extension and should not interfere with the
>>> various legacy boot interfaces.
>>
>> I was just looking at Andrew's patch:
>> http://patchwork.linux-mips.org/patch/9549/
>>
>> How would the other registers (i.e. $a2 and $a3) be defined for this
>> boot interface? I'm guessing any future extensions are envisioned to use
>> a different negative value of $a0, in which case treating them as
>> unused/undefined is fine, but perhaps that should be spelt out in the
>> UHI spec?
> 
> Sounds sensible. Making it explicit may help prevent anyone extending this
> and presuming that they can give meaning to one of the unused registers.
> 
> Did anyone come to a conclusion on physical vs virtual address for the
> DTB? I forgot to reply to the thread, I would have thought the KSEG0
> address would be the obvious choice so that it is immediately usable from
> ordinary memory accesses. However, that is only because I don't follow how
> the kernel would benefit from being given a physical address. It can't be
> remapped except for the case of segmentation control (I believe) so there
> seems little risk in using KSEG0.

The only obvious cases of physical addresses being passed into MIPS
Linux I can find by grepping for fw_arg[0123] are:
bcm3384: for DT boot, expects physical address of dtb in arg2
fw/sni and lantiq: expect physical arg pointer in arg1.

Physical addresses are probably of more use for arches where only
virtual addresses can be accessed after the MMU is turned on, and Linux
is started with the MMU turned off.

I suppose the problems with using virtual addresses for MIPS would be:
* limits it to low 256MB of RAM usually accessible in kseg0 and kseg1
* as you say, slightly less resistant to segmentation changes

I don't think either of those are really significant problems, though I
can see the appeal of physical addresses for this sort of interface. If
however the rest of the UHI boot APIs deal with directly usable
pointers, then maybe its best to stick with that pattern for consistency.

Cheers
James

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Re: [U-Boot] MIPS UHI spec

[Andrew Bresticker]

On Mon, Mar 16, 2015 at 4:53 AM, Matthew Fortune
<Matthew.Fortune@imgtec.com> wrote:
> James Hogan <James.Hogan@imgtec.com> writes:
>> On 26/02/15 12:37, Daniel Schwierzeck wrote:
>> > 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>> >> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>> >>> Hi Daniel,
>> >>>
>> >>> The spec for MIPS Unified Hosting Interface is available here:
>> >>>
>> >>> http://prplfoundation.org/wiki/MIPS_documentation
>> >>>
>> >>> As we have previously discussed, this is an ideal place to define
>> >>> the handover of device tree data from bootloader to kernel. Using a0
>> >>> == -2 and defining which register(s) you need for the actual data
>> >>> will fit nicely. I'll happily include whatever is decided into the
>> >>> next version of the spec.
>> >
>> > this originates from an off-list discussion some months ago started by
>> > John Crispin.
>> >
>> > (CC +John, Ralf, Jonas, linux-mips)
>> >
>> >>
>> >> (CC +Andrew, Ezequiel, James, James)
>> >>
>> >> On the talk of DT handover, this recent patchset adding support for a
>> >> system doing so to Linux is relevant:
>> >>
>> >>
>> >> http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>> >>
>> >> I'm also working on a system for which I'll need to implement DT
>> >> handover very soon. It would be very nice if we could agree on some
>> >> standard way of doing so (and eventually if the code on the Linux
>> >> side can be generic enough to allow a multiplatform kernel).
>> >>
>> >
>> > to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>> > blob. It is a simple extension and should not interfere with the
>> > various legacy boot interfaces.
>>
>> I was just looking at Andrew's patch:
>> http://patchwork.linux-mips.org/patch/9549/
>>
>> How would the other registers (i.e. $a2 and $a3) be defined for this
>> boot interface? I'm guessing any future extensions are envisioned to use
>> a different negative value of $a0, in which case treating them as
>> unused/undefined is fine, but perhaps that should be spelt out in the
>> UHI spec?
>
> Sounds sensible. Making it explicit may help prevent anyone extending this
> and presuming that they can give meaning to one of the unused registers.
>
> Did anyone come to a conclusion on physical vs virtual address for the
> DTB? I forgot to reply to the thread, I would have thought the KSEG0
> address would be the obvious choice so that it is immediately usable from
> ordinary memory accesses. However, that is only because I don't follow how
> the kernel would benefit from being given a physical address. It can't be
> remapped except for the case of segmentation control (I believe) so there
> seems little risk in using KSEG0.

We've changed our bootloader to pass the DTB via KSEG0.  V2 of the
Pistachio platform patches I posted last week used this protocol.

Thanks,
Andrew

[U-Boot] MIPS UHI spec

[Andrew Bresticker]

On Mon, Mar 16, 2015 at 4:53 AM, Matthew Fortune
<Matthew.Fortune@imgtec.com> wrote:
> James Hogan <James.Hogan@imgtec.com> writes:
>> On 26/02/15 12:37, Daniel Schwierzeck wrote:
>> > 2015-02-26 11:17 GMT+01:00 Paul Burton <paul.burton@imgtec.com>:
>> >> On Thu, Feb 19, 2015 at 01:50:23PM +0000, Matthew Fortune wrote:
>> >>> Hi Daniel,
>> >>>
>> >>> The spec for MIPS Unified Hosting Interface is available here:
>> >>>
>> >>> http://prplfoundation.org/wiki/MIPS_documentation
>> >>>
>> >>> As we have previously discussed, this is an ideal place to define
>> >>> the handover of device tree data from bootloader to kernel. Using a0
>> >>> == -2 and defining which register(s) you need for the actual data
>> >>> will fit nicely. I'll happily include whatever is decided into the
>> >>> next version of the spec.
>> >
>> > this originates from an off-list discussion some months ago started by
>> > John Crispin.
>> >
>> > (CC +John, Ralf, Jonas, linux-mips)
>> >
>> >>
>> >> (CC +Andrew, Ezequiel, James, James)
>> >>
>> >> On the talk of DT handover, this recent patchset adding support for a
>> >> system doing so to Linux is relevant:
>> >>
>> >>
>> >> http://www.linux-mips.org/archives/linux-mips/2015-02/msg00312.html
>> >>
>> >> I'm also working on a system for which I'll need to implement DT
>> >> handover very soon. It would be very nice if we could agree on some
>> >> standard way of doing so (and eventually if the code on the Linux
>> >> side can be generic enough to allow a multiplatform kernel).
>> >>
>> >
>> > to be conformant with UHI I propose $a0 == -2 and $a1 == address of DT
>> > blob. It is a simple extension and should not interfere with the
>> > various legacy boot interfaces.
>>
>> I was just looking at Andrew's patch:
>> http://patchwork.linux-mips.org/patch/9549/
>>
>> How would the other registers (i.e. $a2 and $a3) be defined for this
>> boot interface? I'm guessing any future extensions are envisioned to use
>> a different negative value of $a0, in which case treating them as
>> unused/undefined is fine, but perhaps that should be spelt out in the
>> UHI spec?
>
> Sounds sensible. Making it explicit may help prevent anyone extending this
> and presuming that they can give meaning to one of the unused registers.
>
> Did anyone come to a conclusion on physical vs virtual address for the
> DTB? I forgot to reply to the thread, I would have thought the KSEG0
> address would be the obvious choice so that it is immediately usable from
> ordinary memory accesses. However, that is only because I don't follow how
> the kernel would benefit from being given a physical address. It can't be
> remapped except for the case of segmentation control (I believe) so there
> seems little risk in using KSEG0.

We've changed our bootloader to pass the DTB via KSEG0.  V2 of the
Pistachio platform patches I posted last week used this protocol.

Thanks,
Andrew