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

[lihuisong (C)]

在 2025/10/27 20:28, Rafael J. Wysocki 写道:
> On Mon, Oct 27, 2025 at 2:43 AM lihuisong (C) <lihuisong@xxxxxxxxxx> wrote:
> > 在 2025/10/26 20:40, Rafael J. Wysocki 写道:
> > > On Fri, Oct 24, 2025 at 11:40 AM lihuisong (C) <lihuisong@xxxxxxxxxx> wrote:
> > > > 在 2025/10/23 18:35, Rafael J. Wysocki 写道:
> > > > > On Thu, Oct 23, 2025 at 12:17 PM lihuisong (C) <lihuisong@xxxxxxxxxx> wrote:
> > > > > > 在 2025/10/22 3:42, Rafael J. Wysocki 写道:
> > > > > > > On Mon, Sep 29, 2025 at 11:38 AM Huisong Li <lihuisong@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > > > > > > ---
> > > > > > > >      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?
Arm64 supports the acpi_processor_ffh_lpi_probe().
So pr->flags.has_lpi is 1 on success.
> > > > 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.
What you mean is that X86 use LPI?
If X86 also define acpi_processor_ffh_lpi_probe and use LPI, this patch 
is also good to it.