linux-kernel - Re: [PATCH v1 5/9] ACPI: processor: idle: Add the verification of processor FFH LPI state

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Message-ID: <CAJZ5v0j9i1W3JmDQP+-tTqu1dnE1i1XeZUk5=JMKRN_e++iJ7w@mail.gmail.com>
Date: Mon, 27 Oct 2025 13:28:30 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "lihuisong (C)" <lihuisong@...wei.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, lenb@...nel.org, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Sudeep.Holla@....com, linuxarm@...wei.com, 
	jonathan.cameron@...wei.com, zhanjie9@...ilicon.com, zhenglifeng1@...wei.com, 
	yubowen8@...wei.com
Subject: Re: [PATCH v1 5/9] ACPI: processor: idle: Add the verification of
 processor FFH LPI state

On Mon, Oct 27, 2025 at 2:43 AM lihuisong (C) <lihuisong@...wei.com> wrote:
>
>
> 在 2025/10/26 20:40, Rafael J. Wysocki 写道:
> > On Fri, Oct 24, 2025 at 11:40 AM lihuisong (C) <lihuisong@...wei.com> wrote:
> >>
> >> 在 2025/10/23 18:35, Rafael J. Wysocki 写道:
> >>> On Thu, Oct 23, 2025 at 12:17 PM lihuisong (C) <lihuisong@...wei.com> wrote:
> >>>> 在 2025/10/22 3:42, Rafael J. Wysocki 写道:
> >>>>> On Mon, Sep 29, 2025 at 11:38 AM Huisong Li <lihuisong@...wei.com> wrote:
> >>>>>> Both ARM64 and RISCV architecture would validate Entry Method of LPI
> >>>>>> state and SBI HSM or PSCI cpu suspend. Driver should return failure
> >>>>>> if FFH of LPI state are not ok.
> >>>>> First of all, I cannot parse this changelog, so I don't know the
> >>>>> motivation for the change.
> >>>> Sorry for your confusion.
> >>>>> Second, if _LPI is ever used on x86, the
> >>>>> acpi_processor_ffh_lpi_probe() in acpi_processor_get_power_info() will
> >>>>> get in the way.
> >>>> AFAICS, it's also ok if X86 platform use LPI.
> >>> No, because it returns an error by default as it stands today.
> >>>
> >>>>> Why does the evaluation in acpi_processor_setup_cpuidle_dev() not work?
> >>>> The acpi_processor_ffh_lpi_probe does verify the validity of LPI for ARM
> >>>> and RISCV.
> >>>> But the caller of the acpi_processor_setup_cpuidle_dev()don't verify the
> >>>> return value.
> >>>> In addition, from the name of acpi_processor_setup_cpuidle_dev(), its
> >>>> main purpose is to setup cpudile device rather than to verify LPI.
> >>> That's fair enough.
> >>>
> >>> Also, the list of idle states belongs to the cpuidle driver, not to a
> >>> cpuidle device.
> >>>
> >>>> So I move it to a more prominent position and redefine the
> >>>> acpi_processor_setup_cpuidle_dev to void in patch 9/9.
> >>>>>> Fixes: a36a7fecfe60 ("ACPI / processor_idle: Add support for Low Power Idle(LPI) states")
> >>>>>> Signed-off-by: Huisong Li <lihuisong@...wei.com>
> >>>>>> ---
> >>>>>>     drivers/acpi/processor_idle.c | 10 ++++++++--
> >>>>>>     1 file changed, 8 insertions(+), 2 deletions(-)
> >>>>>>
> >>>>>> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> >>>>>> index 5684925338b3..b0d6b51ee363 100644
> >>>>>> --- a/drivers/acpi/processor_idle.c
> >>>>>> +++ b/drivers/acpi/processor_idle.c
> >>>>>> @@ -1264,7 +1264,7 @@ static int acpi_processor_setup_cpuidle_dev(struct acpi_processor *pr,
> >>>>>>
> >>>>>>            dev->cpu = pr->id;
> >>>>>>            if (pr->flags.has_lpi)
> >>>>>> -               return acpi_processor_ffh_lpi_probe(pr->id);
> >>>>>> +               return 0;
> >>>>>>
> >>>>>>            return acpi_processor_setup_cpuidle_cx(pr, dev);
> >>>>>>     }
> >>>>>> @@ -1275,7 +1275,13 @@ static int acpi_processor_get_power_info(struct acpi_processor *pr)
> >>>>>>
> >>>>>>            ret = acpi_processor_get_lpi_info(pr);
> >>>>>>            if (ret)
> >>> So I think it would be better to check it here, that is
> >>>
> >>> if (!ret) {
> >>>          ret = acpi_processor_ffh_lpi_probe(pr->id));
> >>>          if (!ret)
> >>>                  return 0;
> >>>
> >>>          pr_info("CPU%d: FFH LPI state is invalid\n", pr->id);
> >>>          pr->flags.has_lpi = 0;
> >>> }
> >>>
> >>> return acpi_processor_get_cstate_info(pr);
> >>>
> >>> And the default acpi_processor_ffh_lpi_probe() needs to be changed to return 0.
> >> Sorry, I don't understand why pr->flags.has_lpi is true if
> >> acpi_processor_ffh_lpi_probe() return failure.
> > It is set by acpi_processor_get_lpi_info() on success and
> > acpi_processor_ffh_lpi_probe() does not update it.
> The acpi_processor_get_lpi_info() will return failure on X86 platform
> because this function first call acpi_processor_ffh_lpi_probe().
> And acpi_processor_ffh_lpi_probe return EOPNOTSUPP because X86 platform
> doesn't implement it.
> So I think pr->flags.has_lpi is false on X86 plaform.

On x86 it is 0, but what if acpi_processor_ffh_lpi_probe() fails on arm64, say?

> >
> >> In addition, X86 platform doesn't define acpi_processor_ffh_lpi_probe().
> >> this function will return EOPNOTSUPP.
> > Which is exactly why it is a problem.  x86 has no reason to implement
> > it because FFH always works there.
> Sorry, I still don't understand why X86 has no reason to implement it.
> I simply think that X86 doesn't need it.
> AFAICS, the platform doesn't need to get LPI info if this platform
> doesn't implement acpi_processor_ffh_lpi_probe().

Well, that's what is implemented in the current code, but it will need
to be changed if x86 is ever added and I'd rather avoid cleanups
making it harder to change.