linux-kernel - Re: [PATCH v2 1/4] ACPI: s2idle: Add a new ->enter() callback for platform_s2idle

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Date:   Mon, 29 Aug 2022 16:20:03 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, Pavel Machek <pavel@....cz>,
        Hans de Goede <hdegoede@...hat.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] ACPI: s2idle: Add a new ->enter() callback for platform_s2idle_ops

On Mon, Aug 29, 2022 at 3:29 PM Mario Limonciello
<mario.limonciello@....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?

> Signed-off-by: Mario Limonciello <mario.limonciello@....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.

>  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
>