PSCI domains without OSI support

PSCI domains without OSI support

[Dmitry Baryshkov]

Hi,

Lately I have been working on improving the msm8996 platform support.
Vendor kernel seems to support domain-like idle (see [1], [2]).
However when I tried changing upstream msm8996.dtsi to use PSCI
domains, I faced the firmware reporting NOT_SUPPORTED to an attempt to
enable OSI (thus rendering PSCI domains useless, as they are now
marked with ALWAYS_ON).

I noticed that vendor kernel makes a call to cpu_suspend() with
power_state following the original format (described in PSCI spec
5.4.2.1). What would be the best way to support this?
- Allow DTS forcing the PSCI power domains even if OSI enablement fails?
- Add a separate cpuidle driver?
- Just forget about it and use plain PSCI as we currently do?

Additional topic: for one of idle states the vendor kernel uses a
proprietary call into the hypervisor ([3]). Up to now we have ignored
this, as 8996 seems to be the only platform using it. I suppose that
adding it to cpuidle-psci.c would be frowned upon. Is this assumption
correct? Would it add another point for adding a separate cpuidle
driver?

[1] https://git.codelinaro.org/clo/la/kernel/msm-3.18/-/blob/LA.UM.6.6.c31-02700-89xx.0/arch/arm/boot/dts/qcom/msm8996-pm.dtsi#L32

[2] https://git.codelinaro.org/clo/la/kernel/msm-3.18/-/blob/LA.UM.6.6.c31-02700-89xx.0/drivers/cpuidle/lpm-levels.c#L927

[3] https://git.codelinaro.org/clo/la/kernel/msm-3.18/-/blob/LA.UM.6.6.c31-02700-89xx.0/drivers/cpuidle/lpm-levels.c#L944

-- 
With best wishes
Dmitry

Re: PSCI domains without OSI support

[Sudeep Holla]

On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
> Hi,
> 
> Lately I have been working on improving the msm8996 platform support.
> Vendor kernel seems to support domain-like idle (see [1], [2]).
> However when I tried changing upstream msm8996.dtsi to use PSCI
> domains, I faced the firmware reporting NOT_SUPPORTED to an attempt to
> enable OSI (thus rendering PSCI domains useless, as they are now
> marked with ALWAYS_ON).
>

That's not good to hear 🙁.

> I noticed that vendor kernel makes a call to cpu_suspend() with
> power_state following the original format (described in PSCI spec
> 5.4.2.1). What would be the best way to support this?

And why is this not possible with the existing code ? Not sure if I
understood it right, I am assuming you are mentioning that it is not
possible.

> - Allow DTS forcing the PSCI power domains even if OSI enablement fails?

Meaning DTS flag for this ? If OSI enable fails, why would you want to
still proceed. It is non-compliant and must be fixed if the firmware
supports OSI and expects OSPM to use the same.

> - Add a separate cpuidle driver?

I would avoid that.

> - Just forget about it and use plain PSCI as we currently do?
>

Worst case yes. My main worry is how many of the old SDM SoC has such a
behaviour and how much they wary from each other. The OSI mode was pushed
after lengthy discussions to support all these platforms and now we have
platforms needing separate idle driver ?

> Additional topic: for one of idle states the vendor kernel uses a
> proprietary call into the hypervisor ([3]).

Again I would say it is not spec compliant.

> Up to now we have ignored this, as 8996 seems to be the only platform using
> it. I suppose that adding it to cpuidle-psci.c would be frowned upon.

Indeed.

> Is this assumption correct? Would it add another point for adding a separate
> cpuidle driver?
>

I am getting a sense that this would be cleaner approach but I would like
to understand how much of these non-compliance is carried to the other
relatively newer SoCs. I understand this is atleast 5-6+ years old. I don't
want this to set example to deviate from standard driver by adding new
drivers though they all are supposedly using PSCI(and are not fully compliant)

-- 
Regards,
Sudeep

Re: PSCI domains without OSI support

[Dmitry Baryshkov]

On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
> > Hi,
> >
> > Lately I have been working on improving the msm8996 platform support.
> > Vendor kernel seems to support domain-like idle (see [1], [2]).
> > However when I tried changing upstream msm8996.dtsi to use PSCI
> > domains, I faced the firmware reporting NOT_SUPPORTED to an attempt to
> > enable OSI (thus rendering PSCI domains useless, as they are now
> > marked with ALWAYS_ON).
> >
>
> That's not good to hear 🙁.
>
> > I noticed that vendor kernel makes a call to cpu_suspend() with
> > power_state following the original format (described in PSCI spec
> > 5.4.2.1). What would be the best way to support this?
>
> And why is this not possible with the existing code ? Not sure if I
> understood it right, I am assuming you are mentioning that it is not
> possible.

It's not possible with the cpuidle-psci-domains.c. The driver marks
all genpds as ALWAYS_ON, thus making sure that they are never
suspended.

> > - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
>
> Meaning DTS flag for this ? If OSI enable fails, why would you want to
> still proceed. It is non-compliant and must be fixed if the firmware
> supports OSI and expects OSPM to use the same.

I'm not sure at this moment. PSCI firmware reports that OSI mode is
supported, but then when psci_pd_try_set_osi_mode() tries to switch
into OSI mode, it gets NOT_SUPPORTED.
Just for the sake of completeness, I added a print to the psci.c to
dump the result of the psci_set_osi_mode(false). It also returns
NOT_SUPPORTED!

My logical assumption would be that the firmware reports support for
OS_INITIATED, but then just fails to properly support
SET_SUSPEND_MODE.
I should probably try ignoring the error psci-domain.c and continue
with binding power domains. What would be the best way to check that
the domains setup works as expected?

>
> > - Add a separate cpuidle driver?
>
> I would avoid that.
>
> > - Just forget about it and use plain PSCI as we currently do?
> >
>
> Worst case yes. My main worry is how many of the old SDM SoC has such a
> behaviour and how much they wary from each other. The OSI mode was pushed
> after lengthy discussions to support all these platforms and now we have
> platforms needing separate idle driver ?

I'm not sure. 32-bit SoCs use non-PSCI idle driver. MSM8916, sdm845
and later SoCs are using proper domains support.
I tested the sdm660, it looks like it can work with the power domains.
So this leaves only MSM8992/4/8 in question (at least from the
platforms that are supported by the mainline).

>
> > Additional topic: for one of idle states the vendor kernel uses a
> > proprietary call into the hypervisor ([3]).
>
> Again I would say it is not spec compliant.

Yes, of course. Otherwise there would not be such a question.
Judging from the vendor kernels, this call is limited to 8996 only.

>
> > Up to now we have ignored this, as 8996 seems to be the only platform using
> > it. I suppose that adding it to cpuidle-psci.c would be frowned upon.
>
> Indeed.
>
> > Is this assumption correct? Would it add another point for adding a separate
> > cpuidle driver?
> >
>
> I am getting a sense that this would be cleaner approach but I would like
> to understand how much of these non-compliance is carried to the other
> relatively newer SoCs. I understand this is atleast 5-6+ years old. I don't
> want this to set example to deviate from standard driver by adding new
> drivers though they all are supposedly using PSCI(and are not fully compliant)

At this moment I fear that it might be limited to msm8996 only. Maybe
including 8992/4/8.

-- 
With best wishes
Dmitry

Re: PSCI domains without OSI support

[Dmitry Baryshkov]

On Wed, 27 Jul 2022 at 16:24, Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
> >
> > On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:

> > > - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
> >
> > Meaning DTS flag for this ? If OSI enable fails, why would you want to
> > still proceed. It is non-compliant and must be fixed if the firmware
> > supports OSI and expects OSPM to use the same.
>
> I'm not sure at this moment. PSCI firmware reports that OSI mode is
> supported, but then when psci_pd_try_set_osi_mode() tries to switch
> into OSI mode, it gets NOT_SUPPORTED.
> Just for the sake of completeness, I added a print to the psci.c to
> dump the result of the psci_set_osi_mode(false). It also returns
> NOT_SUPPORTED!
>
> My logical assumption would be that the firmware reports support for
> OS_INITIATED, but then just fails to properly support
> SET_SUSPEND_MODE.

Okay. From the msm-3.14 commit log:

Add support to terminate all low power modes in PSCI. The lpm-levels will
work with version 1.0 of PSCI specification using the OS initiated scheme.
The lpm-levels driver would determine the last man standing and vote into
TZ accordingly.

Which means that the vendor kernel expected to work in the OSI mode
without calling SET_SUSPEND (such call doesn't exist in 3.14)

So, this looks like the "force-psci-domains" or "ignore-osi-error"
flag would be logical.
The question about testing still holds.

> I should probably try ignoring the error psci-domain.c and continue
> with binding power domains. What would be the best way to check that
> the domains setup works as expected?

-- 
With best wishes
Dmitry

Re: PSCI domains without OSI support

[Dmitry Baryshkov]

On Wed, 27 Jul 2022 at 16:39, Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> On Wed, 27 Jul 2022 at 16:24, Dmitry Baryshkov
> <dmitry.baryshkov@linaro.org> wrote:
> >
> > On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
> > >
> > > On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
>
> > > > - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
> > >
> > > Meaning DTS flag for this ? If OSI enable fails, why would you want to
> > > still proceed. It is non-compliant and must be fixed if the firmware
> > > supports OSI and expects OSPM to use the same.
> >
> > I'm not sure at this moment. PSCI firmware reports that OSI mode is
> > supported, but then when psci_pd_try_set_osi_mode() tries to switch
> > into OSI mode, it gets NOT_SUPPORTED.
> > Just for the sake of completeness, I added a print to the psci.c to
> > dump the result of the psci_set_osi_mode(false). It also returns
> > NOT_SUPPORTED!
> >
> > My logical assumption would be that the firmware reports support for
> > OS_INITIATED, but then just fails to properly support
> > SET_SUSPEND_MODE.
>
> Okay. From the msm-3.14 commit log:
>
> Add support to terminate all low power modes in PSCI. The lpm-levels will
> work with version 1.0 of PSCI specification using the OS initiated scheme.
> The lpm-levels driver would determine the last man standing and vote into
> TZ accordingly.
>
> Which means that the vendor kernel expected to work in the OSI mode
> without calling SET_SUSPEND (such call doesn't exist in 3.14)

After adding the debugfs file, it's clear that this is the case.

Compare msm8996:
PSCIv1.0
SMC Calling Convention v1.0 is assumed
OSI is supported
Extended StateID format is used

vs sdm845:
PSCIv1.1
SMC Calling Convention v1.2
OSI is supported
Extended StateID format is used
CPU_FREEZE is supported
SET_SUSPEND_MODE is supported

Judging by people reporting 'failure to enable OSI mode' on several
other Qualcomm SoCs (msm8976, msm8953), this bug is present on several
older Qualcomm platforms.

>
> So, this looks like the "force-psci-domains" or "ignore-osi-error"
> flag would be logical.
> The question about testing still holds.

-- 
With best wishes
Dmitry

Re: PSCI domains without OSI support

[Sudeep Holla]

On Wed, Jul 27, 2022 at 04:24:22PM +0300, Dmitry Baryshkov wrote:
> On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
> >
> > On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
> > > Hi,
> > >
> > > Lately I have been working on improving the msm8996 platform support.
> > > Vendor kernel seems to support domain-like idle (see [1], [2]).
> > > However when I tried changing upstream msm8996.dtsi to use PSCI
> > > domains, I faced the firmware reporting NOT_SUPPORTED to an attempt to
> > > enable OSI (thus rendering PSCI domains useless, as they are now
> > > marked with ALWAYS_ON).
> > >
> >
> > That's not good to hear 🙁.
> >
> > > I noticed that vendor kernel makes a call to cpu_suspend() with
> > > power_state following the original format (described in PSCI spec
> > > 5.4.2.1). What would be the best way to support this?
> >
> > And why is this not possible with the existing code ? Not sure if I
> > understood it right, I am assuming you are mentioning that it is not
> > possible.
>
> It's not possible with the cpuidle-psci-domains.c. The driver marks
> all genpds as ALWAYS_ON, thus making sure that they are never
> suspended.
>

That doesn't sound correct. I am sure Ulf has tried this on one of SDM
platform for sure when it was merged.

> > > - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
> >
> > Meaning DTS flag for this ? If OSI enable fails, why would you want to
> > still proceed. It is non-compliant and must be fixed if the firmware
> > supports OSI and expects OSPM to use the same.
>
> I'm not sure at this moment. PSCI firmware reports that OSI mode is
> supported, but then when psci_pd_try_set_osi_mode() tries to switch
> into OSI mode, it gets NOT_SUPPORTED.

Yikes, fix the damn broken firmware. That is utter non-sense. I don't
understand why would the firmware authors enable some feature before it
is ready.

> Just for the sake of completeness, I added a print to the psci.c to
> dump the result of the psci_set_osi_mode(false). It also returns
> NOT_SUPPORTED!
>

Well it is simply broken then. Not tested firmware, so please don't
attempt to use OSI if it is so fundamentally broken. I find it hard to
accept the argument that well it works just that the query API is failing.
But what is the guarantee that it is tested well enough. We will end up
adding more quirks after adding one to enable it.

> My logical assumption would be that the firmware reports support for
> OS_INITIATED, but then just fails to properly support
> SET_SUSPEND_MODE.

I knew this argument was coming as I wrote above, sorry I don't buy that.
It is probably one of the early platforms supporting PSCI and not well tested
for conformance. So I am inclined to just say we can't support it.

> I should probably try ignoring the error psci-domain.c and continue
> with binding power domains. What would be the best way to check that
> the domains setup works as expected?
>
> >
> > > - Add a separate cpuidle driver?
> >
> > I would avoid that.
> >
> > > - Just forget about it and use plain PSCI as we currently do?
> > >
> >
> > Worst case yes. My main worry is how many of the old SDM SoC has such a
> > behaviour and how much they wary from each other. The OSI mode was pushed
> > after lengthy discussions to support all these platforms and now we have
> > platforms needing separate idle driver ?
>
> I'm not sure. 32-bit SoCs use non-PSCI idle driver. MSM8916, sdm845
> and later SoCs are using proper domains support.

Yes that is 32-bit, we just support PSCI on 64-bit. No more arguments
there, we had enough in the early days for almost more than a year. We
are not going back to that again.

--
Regards,
Sudeep

Re: PSCI domains without OSI support

[Dmitry Baryshkov]

On Thu, 28 Jul 2022 at 11:40, Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> On Wed, Jul 27, 2022 at 04:24:22PM +0300, Dmitry Baryshkov wrote:
> > On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
> > >
> > > On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
>
> > > > - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
> > >
> > > Meaning DTS flag for this ? If OSI enable fails, why would you want to
> > > still proceed. It is non-compliant and must be fixed if the firmware
> > > supports OSI and expects OSPM to use the same.
> >
> > I'm not sure at this moment. PSCI firmware reports that OSI mode is
> > supported, but then when psci_pd_try_set_osi_mode() tries to switch
> > into OSI mode, it gets NOT_SUPPORTED.
>
> Yikes, fix the damn broken firmware. That is utter non-sense. I don't
> understand why would the firmware authors enable some feature before it
> is ready.
>
> > Just for the sake of completeness, I added a print to the psci.c to
> > dump the result of the psci_set_osi_mode(false). It also returns
> > NOT_SUPPORTED!
> >
>
> Well it is simply broken then. Not tested firmware, so please don't
> attempt to use OSI if it is so fundamentally broken. I find it hard to
> accept the argument that well it works just that the query API is failing.
> But what is the guarantee that it is tested well enough. We will end up
> adding more quirks after adding one to enable it.
>
> > My logical assumption would be that the firmware reports support for
> > OS_INITIATED, but then just fails to properly support
> > SET_SUSPEND_MODE.
>
> I knew this argument was coming as I wrote above, sorry I don't buy that.
> It is probably one of the early platforms supporting PSCI and not well tested
> for conformance. So I am inclined to just say we can't support it.

I have quoted the commit message from the vendor kernel (and the
debugfs entries) in other messages in this thread. It definitely seems
like the platform breaks strict standard conformance by supporting
CPU_SUSPEND, but not the SET_SUSPEND_MODE. Vendor kernel still used
the CPU_SUSPEND with a domain-like approach, expecting to find the
PSCI already being running in the OSI mode. So I'd ask for the ability
to add a flag to DT telling the PSCI_DOMAINS code that the platform is
already running in the OSI mode despite set_osi_mode() returning
NOT_SUPPORTED.

I would not say that this firmware was not tested to work with the
domains approach. The whole bunch of phones/tables were shipped with
this issue being present and the vendor kernel using a tree-wide
approach to cpu/cluster/system states.


--
With best wishes
Dmitry

Re: PSCI domains without OSI support

[Ulf Hansson]

On Wed, 27 Jul 2022 at 22:51, Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> On Wed, 27 Jul 2022 at 16:39, Dmitry Baryshkov
> <dmitry.baryshkov@linaro.org> wrote:
> >
> > On Wed, 27 Jul 2022 at 16:24, Dmitry Baryshkov
> > <dmitry.baryshkov@linaro.org> wrote:
> > >
> > > On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
> > > >
> > > > On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
> >
> > > > > - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
> > > >
> > > > Meaning DTS flag for this ? If OSI enable fails, why would you want to
> > > > still proceed. It is non-compliant and must be fixed if the firmware
> > > > supports OSI and expects OSPM to use the same.
> > >
> > > I'm not sure at this moment. PSCI firmware reports that OSI mode is
> > > supported, but then when psci_pd_try_set_osi_mode() tries to switch
> > > into OSI mode, it gets NOT_SUPPORTED.
> > > Just for the sake of completeness, I added a print to the psci.c to
> > > dump the result of the psci_set_osi_mode(false). It also returns
> > > NOT_SUPPORTED!
> > >
> > > My logical assumption would be that the firmware reports support for
> > > OS_INITIATED, but then just fails to properly support
> > > SET_SUSPEND_MODE.
> >
> > Okay. From the msm-3.14 commit log:
> >
> > Add support to terminate all low power modes in PSCI. The lpm-levels will
> > work with version 1.0 of PSCI specification using the OS initiated scheme.
> > The lpm-levels driver would determine the last man standing and vote into
> > TZ accordingly.
> >
> > Which means that the vendor kernel expected to work in the OSI mode
> > without calling SET_SUSPEND (such call doesn't exist in 3.14)
>
> After adding the debugfs file, it's clear that this is the case.
>
> Compare msm8996:
> PSCIv1.0
> SMC Calling Convention v1.0 is assumed
> OSI is supported
> Extended StateID format is used
>
> vs sdm845:
> PSCIv1.1
> SMC Calling Convention v1.2
> OSI is supported
> Extended StateID format is used
> CPU_FREEZE is supported
> SET_SUSPEND_MODE is supported
>
> Judging by people reporting 'failure to enable OSI mode' on several
> other Qualcomm SoCs (msm8976, msm8953), this bug is present on several
> older Qualcomm platforms.
>
> >
> > So, this looks like the "force-psci-domains" or "ignore-osi-error"
> > flag would be logical.
> > The question about testing still holds.

Alright, so this looks like a deviation from the spec. Nevertheless,
it seems quite simple for us to fix by overriding the FW error, by
adding a new DT flag, in the way you propose.

In principle, I think the new DT flag should avoid us to call
psci_set_osi_mode() in psci_pd_try_set_osi_mode(), but rather just
return true when the flag is set.

In this way, the GENPD_FLAG_ALWAYS_ON will not be set for the genpds
that are created, so things should work as the PSCI FW has OSI mode
enabled.

Kind regards
Uffe

Re: PSCI domains without OSI support

[Ulf Hansson]

On Thu, 28 Jul 2022 at 10:40, Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> On Wed, Jul 27, 2022 at 04:24:22PM +0300, Dmitry Baryshkov wrote:
> > On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
> > >
> > > On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
> > > > Hi,
> > > >
> > > > Lately I have been working on improving the msm8996 platform support.
> > > > Vendor kernel seems to support domain-like idle (see [1], [2]).
> > > > However when I tried changing upstream msm8996.dtsi to use PSCI
> > > > domains, I faced the firmware reporting NOT_SUPPORTED to an attempt to
> > > > enable OSI (thus rendering PSCI domains useless, as they are now
> > > > marked with ALWAYS_ON).
> > > >
> > >
> > > That's not good to hear 🙁.
> > >
> > > > I noticed that vendor kernel makes a call to cpu_suspend() with
> > > > power_state following the original format (described in PSCI spec
> > > > 5.4.2.1). What would be the best way to support this?
> > >
> > > And why is this not possible with the existing code ? Not sure if I
> > > understood it right, I am assuming you are mentioning that it is not
> > > possible.
> >
> > It's not possible with the cpuidle-psci-domains.c. The driver marks
> > all genpds as ALWAYS_ON, thus making sure that they are never
> > suspended.
> >
>
> That doesn't sound correct. I am sure Ulf has tried this on one of SDM
> platform for sure when it was merged.

It looks like there may be some misunderstanding here.

I think the point Dmitry is trying to make, is that the we set the
GENPD_FLAG_ALWAYS_ON for the created genpds, when the OSI mode could
not be turned on, when probing the cpuidle-psci-domain driver. In this
way, all of cluster idle-states become disabled.

More details about why we have this behaviour can be found from the
commit below.

70c179b49870 ("cpuidle: psci: Allow PM domain to be initialized even
if no OSI mode")

>
> > > > - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
> > >
> > > Meaning DTS flag for this ? If OSI enable fails, why would you want to
> > > still proceed. It is non-compliant and must be fixed if the firmware
> > > supports OSI and expects OSPM to use the same.
> >
> > I'm not sure at this moment. PSCI firmware reports that OSI mode is
> > supported, but then when psci_pd_try_set_osi_mode() tries to switch
> > into OSI mode, it gets NOT_SUPPORTED.
>
> Yikes, fix the damn broken firmware. That is utter non-sense. I don't
> understand why would the firmware authors enable some feature before it
> is ready.

I certainly agree that the FW is broken and should really have been
fixed, but that seems unlikely to happen when moving forward.

On the other hand, it's quite common that we try to add workarounds at
the Linux side to fix FW issues. Of course, it depends on what kind of
hacks it means for us to carry.

In this particular case, I am of the opinion that it looks like the
"hack" may be worth it. Unless I have underestimated the problem, it
seems like a new DT property/flag and a simple if-clause in
psci_pd_try_set_osi_mode() should do the trick for us.

I wouldn't mind maintaining such small parts, when going forward - and
of course I think we should also reject any newer platforms from using
it.

>
> > Just for the sake of completeness, I added a print to the psci.c to
> > dump the result of the psci_set_osi_mode(false). It also returns
> > NOT_SUPPORTED!
> >
>
> Well it is simply broken then. Not tested firmware, so please don't
> attempt to use OSI if it is so fundamentally broken. I find it hard to
> accept the argument that well it works just that the query API is failing.
> But what is the guarantee that it is tested well enough. We will end up
> adding more quirks after adding one to enable it.
>
> > My logical assumption would be that the firmware reports support for
> > OS_INITIATED, but then just fails to properly support
> > SET_SUSPEND_MODE.
>
> I knew this argument was coming as I wrote above, sorry I don't buy that.
> It is probably one of the early platforms supporting PSCI and not well tested
> for conformance. So I am inclined to just say we can't support it.
>

As Dmitry also wrote in his other reply, the FW has certainly been
well tested with the cluster idle states (acting like OSI mode has
been enabled).

To me, it seems like a pity, if we just decided to leave all those
devices out there in the field, lacking support for deeper idle
states. Don't you think?

Kind regards
Uffe

Re: PSCI domains without OSI support

[Sudeep Holla]

On Fri, Aug 05, 2022 at 04:12:42PM +0200, Ulf Hansson wrote:
> On Thu, 28 Jul 2022 at 10:40, Sudeep Holla <sudeep.holla@arm.com> wrote:
> >
> > On Wed, Jul 27, 2022 at 04:24:22PM +0300, Dmitry Baryshkov wrote:
> > > On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
> > > >
> > > > On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
> > > > > Hi,
> > > > >
> > > > > Lately I have been working on improving the msm8996 platform support.
> > > > > Vendor kernel seems to support domain-like idle (see [1], [2]).
> > > > > However when I tried changing upstream msm8996.dtsi to use PSCI
> > > > > domains, I faced the firmware reporting NOT_SUPPORTED to an attempt to
> > > > > enable OSI (thus rendering PSCI domains useless, as they are now
> > > > > marked with ALWAYS_ON).
> > > > >
> > > >
> > > > That's not good to hear 🙁.
> > > >
> > > > > I noticed that vendor kernel makes a call to cpu_suspend() with
> > > > > power_state following the original format (described in PSCI spec
> > > > > 5.4.2.1). What would be the best way to support this?
> > > >
> > > > And why is this not possible with the existing code ? Not sure if I
> > > > understood it right, I am assuming you are mentioning that it is not
> > > > possible.
> > >
> > > It's not possible with the cpuidle-psci-domains.c. The driver marks
> > > all genpds as ALWAYS_ON, thus making sure that they are never
> > > suspended.
> > >
> >
> > That doesn't sound correct. I am sure Ulf has tried this on one of SDM
> > platform for sure when it was merged.
>
> It looks like there may be some misunderstanding here.
>
> I think the point Dmitry is trying to make, is that the we set the
> GENPD_FLAG_ALWAYS_ON for the created genpds, when the OSI mode could
> not be turned on, when probing the cpuidle-psci-domain driver. In this
> way, all of cluster idle-states become disabled.
>
> More details about why we have this behaviour can be found from the
> commit below.
>
> 70c179b49870 ("cpuidle: psci: Allow PM domain to be initialized even
> if no OSI mode")
>

Ah OK, understood now.

> >
> > > > > - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
> > > >
> > > > Meaning DTS flag for this ? If OSI enable fails, why would you want to
> > > > still proceed. It is non-compliant and must be fixed if the firmware
> > > > supports OSI and expects OSPM to use the same.
> > >
> > > I'm not sure at this moment. PSCI firmware reports that OSI mode is
> > > supported, but then when psci_pd_try_set_osi_mode() tries to switch
> > > into OSI mode, it gets NOT_SUPPORTED.
> >
> > Yikes, fix the damn broken firmware. That is utter non-sense. I don't
> > understand why would the firmware authors enable some feature before it
> > is ready.
>
> I certainly agree that the FW is broken and should really have been
> fixed, but that seems unlikely to happen when moving forward.
>
> On the other hand, it's quite common that we try to add workarounds at
> the Linux side to fix FW issues. Of course, it depends on what kind of
> hacks it means for us to carry.
>
> In this particular case, I am of the opinion that it looks like the
> "hack" may be worth it. Unless I have underestimated the problem, it
> seems like a new DT property/flag and a simple if-clause in
> psci_pd_try_set_osi_mode() should do the trick for us.
>

I don't like the idea of new property/flag for this for simple reason.
Once you have that it is impossible to control if downstream new platforms
are using it and they will expect it to be maintained once they ship the
product.

> I wouldn't mind maintaining such small parts, when going forward - and
> of course I think we should also reject any newer platforms from using
> it.
>

The only way that we can achieve this IMO is to have quirks based on
platform compatible which needs to be updated and can be rejected for
newer platforms. New flags means new feature which is expected to be
supported for long and hard to control newer platforms not using them.

> >
> > > Just for the sake of completeness, I added a print to the psci.c to
> > > dump the result of the psci_set_osi_mode(false). It also returns
> > > NOT_SUPPORTED!
> > >
> >
> > Well it is simply broken then. Not tested firmware, so please don't
> > attempt to use OSI if it is so fundamentally broken. I find it hard to
> > accept the argument that well it works just that the query API is failing.
> > But what is the guarantee that it is tested well enough. We will end up
> > adding more quirks after adding one to enable it.
> >
> > > My logical assumption would be that the firmware reports support for
> > > OS_INITIATED, but then just fails to properly support
> > > SET_SUSPEND_MODE.
> >
> > I knew this argument was coming as I wrote above, sorry I don't buy that.
> > It is probably one of the early platforms supporting PSCI and not well tested
> > for conformance. So I am inclined to just say we can't support it.
> >
>
> As Dmitry also wrote in his other reply, the FW has certainly been
> well tested with the cluster idle states (acting like OSI mode has
> been enabled).
>

OK, fair enough if you are aware that is the case here.

> To me, it seems like a pity, if we just decided to leave all those
> devices out there in the field, lacking support for deeper idle
> states. Don't you think?
>

Sure, but I don't like new flags for handling this for reasons stated
above. Unless DT maintainers expect to take "new flag/property" for
some reasons that I am not aware of, I prefer the check on existing
platform compatible to deal with this problem so that this problem
doesn't trickle down to newer platforms as well. Thoughts ?

And please add that we can't add any compatibles that are added later
than certain date to that list when we are adding this support.

--
Regards,
Sudeep

Re: PSCI domains without OSI support

[Dmitry Baryshkov]

On 05/08/2022 19:00, Sudeep Holla wrote:
> On Fri, Aug 05, 2022 at 04:12:42PM +0200, Ulf Hansson wrote:
>> On Thu, 28 Jul 2022 at 10:40, Sudeep Holla <sudeep.holla@arm.com> wrote:
>>>
>>> On Wed, Jul 27, 2022 at 04:24:22PM +0300, Dmitry Baryshkov wrote:
>>>> On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
>>>>>
>>>>> On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
>>>>>> - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
>>>>>
>>>>> Meaning DTS flag for this ? If OSI enable fails, why would you want to
>>>>> still proceed. It is non-compliant and must be fixed if the firmware
>>>>> supports OSI and expects OSPM to use the same.
>>>>
>>>> I'm not sure at this moment. PSCI firmware reports that OSI mode is
>>>> supported, but then when psci_pd_try_set_osi_mode() tries to switch
>>>> into OSI mode, it gets NOT_SUPPORTED.
>>>
>>> Yikes, fix the damn broken firmware. That is utter non-sense. I don't
>>> understand why would the firmware authors enable some feature before it
>>> is ready.
>>
>> I certainly agree that the FW is broken and should really have been
>> fixed, but that seems unlikely to happen when moving forward.
>>
>> On the other hand, it's quite common that we try to add workarounds at
>> the Linux side to fix FW issues. Of course, it depends on what kind of
>> hacks it means for us to carry.
>>
>> In this particular case, I am of the opinion that it looks like the
>> "hack" may be worth it. Unless I have underestimated the problem, it
>> seems like a new DT property/flag and a simple if-clause in
>> psci_pd_try_set_osi_mode() should do the trick for us.
>>
> 
> I don't like the idea of new property/flag for this for simple reason.
> Once you have that it is impossible to control if downstream new platforms
> are using it and they will expect it to be maintained once they ship the
> product.

According to my quick research the requested issue was present on 
platforms revealed from 2015 (2013?) to 2017. Since sdm845 (December 
2017) the issue is not present. So this is a part of history rather than 
current platforms being in need of this quirk.

> 
>> I wouldn't mind maintaining such small parts, when going forward - and
>> of course I think we should also reject any newer platforms from using
>> it.
>>
> 
> The only way that we can achieve this IMO is to have quirks based on
> platform compatible which needs to be updated and can be rejected for
> newer platforms. New flags means new feature which is expected to be
> supported for long and hard to control newer platforms not using them.

I see your point. However from my point of view, the DT property allows 
more finer-grained control.

Compare the semantics:
- Proprety: assume that the platform is in OSI mode, do not call 
psci_osi_set_mode().

- Platform compat list: If the psci_osi_set_mode() has failed, ignore 
the error. I would not dare to blindly assume that e.g. all msm8996 
devices are in OSI mode.

[skipped]

>> To me, it seems like a pity, if we just decided to leave all those
>> devices out there in the field, lacking support for deeper idle
>> states. Don't you think?
>>
> 
> Sure, but I don't like new flags for handling this for reasons stated
> above. Unless DT maintainers expect to take "new flag/property" for
> some reasons that I am not aware of, I prefer the check on existing
> platform compatible to deal with this problem so that this problem
> doesn't trickle down to newer platforms as well. Thoughts ?
> 
> And please add that we can't add any compatibles that are added later
> than certain date to that list when we are adding this support.

Then we are ruling out existing platforms, which are not yet supported 
by Linux. Hopefully you meant that we can not extend this list with 
platforms developed/announced after certain date (I might be slightly 
wrong here, but I estimate that the end of 2018 as a safe boundary).

Newer platforms (sdm845, 2018, qcs404, 2019, etc) report SET_SUSPEND as 
supported (and return DENIED in attempt to set the PC mode).

-- 
With best wishes
Dmitry

Re: PSCI domains without OSI support

[Ulf Hansson]

On Fri, 5 Aug 2022 at 23:39, Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> On 05/08/2022 19:00, Sudeep Holla wrote:
> > On Fri, Aug 05, 2022 at 04:12:42PM +0200, Ulf Hansson wrote:
> >> On Thu, 28 Jul 2022 at 10:40, Sudeep Holla <sudeep.holla@arm.com> wrote:
> >>>
> >>> On Wed, Jul 27, 2022 at 04:24:22PM +0300, Dmitry Baryshkov wrote:
> >>>> On Wed, 27 Jul 2022 at 14:14, Sudeep Holla <sudeep.holla@arm.com> wrote:
> >>>>>
> >>>>> On Wed, Jul 27, 2022 at 12:09:27PM +0300, Dmitry Baryshkov wrote:
> >>>>>> - Allow DTS forcing the PSCI power domains even if OSI enablement fails?
> >>>>>
> >>>>> Meaning DTS flag for this ? If OSI enable fails, why would you want to
> >>>>> still proceed. It is non-compliant and must be fixed if the firmware
> >>>>> supports OSI and expects OSPM to use the same.
> >>>>
> >>>> I'm not sure at this moment. PSCI firmware reports that OSI mode is
> >>>> supported, but then when psci_pd_try_set_osi_mode() tries to switch
> >>>> into OSI mode, it gets NOT_SUPPORTED.
> >>>
> >>> Yikes, fix the damn broken firmware. That is utter non-sense. I don't
> >>> understand why would the firmware authors enable some feature before it
> >>> is ready.
> >>
> >> I certainly agree that the FW is broken and should really have been
> >> fixed, but that seems unlikely to happen when moving forward.
> >>
> >> On the other hand, it's quite common that we try to add workarounds at
> >> the Linux side to fix FW issues. Of course, it depends on what kind of
> >> hacks it means for us to carry.
> >>
> >> In this particular case, I am of the opinion that it looks like the
> >> "hack" may be worth it. Unless I have underestimated the problem, it
> >> seems like a new DT property/flag and a simple if-clause in
> >> psci_pd_try_set_osi_mode() should do the trick for us.
> >>
> >
> > I don't like the idea of new property/flag for this for simple reason.
> > Once you have that it is impossible to control if downstream new platforms
> > are using it and they will expect it to be maintained once they ship the
> > product.
>
> According to my quick research the requested issue was present on
> platforms revealed from 2015 (2013?) to 2017. Since sdm845 (December
> 2017) the issue is not present. So this is a part of history rather than
> current platforms being in need of this quirk.
>
> >
> >> I wouldn't mind maintaining such small parts, when going forward - and
> >> of course I think we should also reject any newer platforms from using
> >> it.
> >>
> >
> > The only way that we can achieve this IMO is to have quirks based on
> > platform compatible which needs to be updated and can be rejected for
> > newer platforms. New flags means new feature which is expected to be
> > supported for long and hard to control newer platforms not using them.
>
> I see your point. However from my point of view, the DT property allows
> more finer-grained control.

It does, but perhaps it's not really needed, as you indicate below?

I share Sudeep's concerns about future possible abuse, so if we think
we can get the "compat list approach" to work, that sounds better for
me too.

>
> Compare the semantics:
> - Proprety: assume that the platform is in OSI mode, do not call
> psci_osi_set_mode().
>
> - Platform compat list: If the psci_osi_set_mode() has failed, ignore
> the error. I would not dare to blindly assume that e.g. all msm8996
> devices are in OSI mode.

You have a point!

So it looks safer to ignore the error that is returned from
psci_osi_set_mode(), rather than skipping to call it (maybe we want to
log a warning when it fails though?).

[...]

Kind regards
Uffe