Re: [PATCH v2 1/4] ACPI: s2idle: Add a new ->enter() callback for platform_s2idle_ops

["Limonciello, Mario" <mario.limonciello@amd.com>]

On 8/29/2022 09:40, Rafael J. Wysocki wrote:
> On Mon, Aug 29, 2022 at 4:32 PM Limonciello, Mario
> <mario.limonciello@amd.com> wrote:
>>
>> On 8/29/2022 09:20, Rafael J. Wysocki wrote:
>>> On Mon, Aug 29, 2022 at 3:29 PM Mario Limonciello
>>> <mario.limonciello@amd.com> wrote:
>>>>
>>>> On some platforms it is found that Linux more aggressively enters s2idle
>>>> than Windows enters Modern Standby and this uncovers some synchronization
>>>> issues for the platform.  To aid in debugging this class of problems in
>>>> the future, add support for an extra optional callback intended for
>>>> drivers to emit extra debugging.
>>>
>>> I'm not liking this.
>>>
>>> If you want debug, why not simply add it where it is needed?
>>
>> Actually this is exactly where it's needed.  The synchronization issue
>> is with what non-x86 is doing while x86 transitions into ACPI C3.
> 
> I meant directly, without adding new driver callbacks.  Adding
> callbacks for debug only seems a bit excessive.
> 
> But I guess the problem is that you need to ask the PMC about
> something then, don't you?

Yeah, that's exactly it.  The code changes there won't make sense 
generically.  I suppose it's possible to make a global symbol and only 
call it in the AMD case, but this approach should be a lot cleaner.

I did CC you in the other 3 patches in the series (in platform-x86) so 
you can see exactly how it's used.  Patch 4/4 is the one that uses this.

https://patchwork.kernel.org/project/platform-driver-x86/patch/20220829132908.5254-5-mario.limonciello@amd.com/

> 
>>>
>>>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>>>> ---
>>>> v1->v2:
>>>>    * Add a prototype for `acpi_s2idle_enter`
>>>>
>>>>    drivers/acpi/sleep.h      |  1 +
>>>>    drivers/acpi/x86/s2idle.c | 14 ++++++++++++++
>>>>    include/linux/acpi.h      |  1 +
>>>>    include/linux/suspend.h   |  1 +
>>>>    kernel/power/suspend.c    |  3 +++
>>>>    5 files changed, 20 insertions(+)
>>>>
>>>> diff --git a/drivers/acpi/sleep.h b/drivers/acpi/sleep.h
>>>> index 7fe41ee489d6..7856930a7da9 100644
>>>> --- a/drivers/acpi/sleep.h
>>>> +++ b/drivers/acpi/sleep.h
>>>> @@ -18,6 +18,7 @@ static inline acpi_status acpi_set_waking_vector(u32 wakeup_address)
>>>>    extern int acpi_s2idle_begin(void);
>>>>    extern int acpi_s2idle_prepare(void);
>>>>    extern int acpi_s2idle_prepare_late(void);
>>>> +extern void acpi_s2idle_enter(void);
>>>
>>> And this name is confusing, because it suggests that the role of the
>>> callback is to make the platform enter s2idle which isn't the case.
>>
>> Can you propose another name?
> 
> acpi_s2idle_check() or similar.

OK, will plan to change over to this name for v3.

> 
>>>
>>>>    extern bool acpi_s2idle_wake(void);
>>>>    extern void acpi_s2idle_restore_early(void);
>>>>    extern void acpi_s2idle_restore(void);
>>>> diff --git a/drivers/acpi/x86/s2idle.c b/drivers/acpi/x86/s2idle.c
>>>> index f9ac12b778e6..c984093a3657 100644
>>>> --- a/drivers/acpi/x86/s2idle.c
>>>> +++ b/drivers/acpi/x86/s2idle.c
>>>> @@ -486,6 +486,19 @@ int acpi_s2idle_prepare_late(void)
>>>>           return 0;
>>>>    }
>>>>
>>>> +void acpi_s2idle_enter(void)
>>>> +{
>>>> +       struct acpi_s2idle_dev_ops *handler;
>>>> +
>>>> +       if (!lps0_device_handle || sleep_no_lps0)
>>>> +               return;
>>>> +
>>>> +       list_for_each_entry(handler, &lps0_s2idle_devops_head, list_node) {
>>>> +               if (handler->enter)
>>>> +                       handler->enter();
>>>> +       }
>>>> +}
>>>> +
>>>>    void acpi_s2idle_restore_early(void)
>>>>    {
>>>>           struct acpi_s2idle_dev_ops *handler;
>>>> @@ -527,6 +540,7 @@ static const struct platform_s2idle_ops acpi_s2idle_ops_lps0 = {
>>>>           .begin = acpi_s2idle_begin,
>>>>           .prepare = acpi_s2idle_prepare,
>>>>           .prepare_late = acpi_s2idle_prepare_late,
>>>> +       .enter = acpi_s2idle_enter,
>>>>           .wake = acpi_s2idle_wake,
>>>>           .restore_early = acpi_s2idle_restore_early,
>>>>           .restore = acpi_s2idle_restore,
>>>> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
>>>> index 6f64b2f3dc54..9df14b5a875c 100644
>>>> --- a/include/linux/acpi.h
>>>> +++ b/include/linux/acpi.h
>>>> @@ -1076,6 +1076,7 @@ struct acpi_s2idle_dev_ops {
>>>>           struct list_head list_node;
>>>>           void (*prepare)(void);
>>>>           void (*restore)(void);
>>>> +       void (*enter)(void);
>>>>    };
>>>>    int acpi_register_lps0_dev(struct acpi_s2idle_dev_ops *arg);
>>>>    void acpi_unregister_lps0_dev(struct acpi_s2idle_dev_ops *arg);
>>>> diff --git a/include/linux/suspend.h b/include/linux/suspend.h
>>>> index 70f2921e2e70..5a3fdca0a628 100644
>>>> --- a/include/linux/suspend.h
>>>> +++ b/include/linux/suspend.h
>>>> @@ -191,6 +191,7 @@ struct platform_s2idle_ops {
>>>>           int (*begin)(void);
>>>>           int (*prepare)(void);
>>>>           int (*prepare_late)(void);
>>>> +       void (*enter)(void);
>>>>           bool (*wake)(void);
>>>>           void (*restore_early)(void);
>>>>           void (*restore)(void);
>>>> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
>>>> index 827075944d28..0c08032d6b50 100644
>>>> --- a/kernel/power/suspend.c
>>>> +++ b/kernel/power/suspend.c
>>>> @@ -136,6 +136,9 @@ static void s2idle_loop(void)
>>>>                           break;
>>>>                   }
>>>>
>>>> +               if (s2idle_ops && s2idle_ops->enter)
>>>> +                       s2idle_ops->enter();
>>>> +
>>>>                   s2idle_enter();
>>>>           }
>>>>
>>>> --