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 09:20, 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.

> 
>> 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?

> 
>>   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();
>>          }
>>
>> --
>> 2.34.1
>>