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 16:40:01 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Limonciello, Mario" <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 4:32 PM Limonciello, Mario
<mario.limonciello@....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@....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?

> >
> >> 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.
>
> Can you propose another name?

acpi_s2idle_check() or similar.

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