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

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Message-ID: <CAJZ5v0hHO_vuQ71sQ2=vmjEMNr3jYh6Wx_nk55gQVdGgWFDHKQ@mail.gmail.com>
Date: Sun, 26 Oct 2025 13:40:14 +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 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.

> 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.

> >
> >>>> -               ret = acpi_processor_get_cstate_info(pr);
> >>>> +               return acpi_processor_get_cstate_info(pr);
> >>>> +
> >>>> +       if (pr->flags.has_lpi) {
> >>>> +               ret = acpi_processor_ffh_lpi_probe(pr->id);
> >>>> +               if (ret)
> >>>> +                       pr_err("Processor FFH LPI state is invalid.\n");
> >>>> +       }
> >>>>
> >>>>           return ret;
> >>>>    }
> >>>> --