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

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Message-ID: <8b1dc682-928a-4898-876c-ae6ccf59d328@huawei.com>
Date: Tue, 28 Oct 2025 20:45:15 +0800
From: "lihuisong (C)" <lihuisong@...wei.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
CC: <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


在 2025/10/27 20:28, Rafael J. Wysocki 写道:
> 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?
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.