Date:	Fri, 4 Mar 2016 11:34:40 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
Cc:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Kevin Hilman <khilman@...nel.org>,
	linux-renesas-soc@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH] PM / Runtime: Only force-resume device if it has been force-suspended

+ Alan

On 3 March 2016 at 21:16, Laurent Pinchart
<laurent.pinchart+renesas@...asonboard.com> wrote:
> The pm_runtime_force_suspend() and pm_runtime_force_resume() helpers are
> designed to help driver being RPM-centric by offering an easy way to
> manager runtime PM state during system suspend and resume. The first
> function will force the device into runtime suspend at system suspend
> time, while the second one will perform the reverse operation at system
> resume time.
>
> However, the pm_runtime_force_resume() really forces resume, regarding
> of whether the device was running or already suspended before the call
> to pm_runtime_force_suspend(). This results in devices being runtime
> resumed at system resume time when they shouldn't.
>
> Fix this by recording whether the device has been forcefully suspended
> in pm_runtime_force_suspend() and condition resume in
> pm_runtime_force_resume() to that state.
>
> All current users of pm_runtime_force_resume() call the function
> uncontionally in their system resume handler (some actually set it as
> the resume handler), all after calling pm_runtime_force_suspend() at
> system suspend time. The change in behaviour should thus be safe.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> ---
>  drivers/base/power/runtime.c | 12 +++++++++---
>  include/linux/pm.h           |  1 +
>  2 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 4c7055009bd6..ad2189294c9b 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1400,6 +1400,7 @@ void pm_runtime_init(struct device *dev)
>         pm_suspend_ignore_children(dev, false);
>         dev->power.runtime_auto = true;
>
> +       dev->power.is_force_suspended = false;
>         dev->power.request_pending = false;
>         dev->power.request = RPM_REQ_NONE;
>         dev->power.deferred_resume = false;
> @@ -1475,6 +1476,7 @@ int pm_runtime_force_suspend(struct device *dev)
>                 goto err;
>
>         pm_runtime_set_suspended(dev);
> +       dev->power.is_force_suspended = true;
>         return 0;
>  err:
>         pm_runtime_enable(dev);
> @@ -1483,13 +1485,13 @@ err:
>  EXPORT_SYMBOL_GPL(pm_runtime_force_suspend);
>
>  /**
> - * pm_runtime_force_resume - Force a device into resume state.
> + * pm_runtime_force_resume - Force a device into resume state if needed.
>   * @dev: Device to resume.
>   *
>   * Prior invoking this function we expect the user to have brought the device
>   * into low power state by a call to pm_runtime_force_suspend(). Here we reverse
> - * those actions and brings the device into full power. We update the runtime PM
> - * status and re-enables runtime PM.
> + * those actions and bring the device back to its runtime PM state before forced
> + * suspension. We update the runtime PM status and re-enables runtime PM.
>   *
>   * Typically this function may be invoked from a system resume callback to make
>   * sure the device is put into full power state.
> @@ -1499,6 +1501,9 @@ int pm_runtime_force_resume(struct device *dev)
>         int (*callback)(struct device *);
>         int ret = 0;
>
> +       if (!dev->power.is_force_suspended)
> +               goto out;
> +
>         callback = RPM_GET_CALLBACK(dev, runtime_resume);
>
>         if (!callback) {
> @@ -1510,6 +1515,7 @@ int pm_runtime_force_resume(struct device *dev)
>         if (ret)
>                 goto out;
>
> +       dev->power.is_force_suspended = false;
>         pm_runtime_set_active(dev);
>         pm_runtime_mark_last_busy(dev);
>  out:
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 6a5d654f4447..bec15e0f244e 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -596,6 +596,7 @@ struct dev_pm_info {
>         unsigned int            use_autosuspend:1;
>         unsigned int            timer_autosuspends:1;
>         unsigned int            memalloc_noio:1;
> +       unsigned int            is_force_suspended:1;
>         enum rpm_request        request;
>         enum rpm_status         runtime_status;
>         int                     runtime_error;
> --

Overall I have no objections to this change, as I think it's improving
the behaviour!

What I was thinking though, but it might be a bit controversial. :-)...
Instead of relying on whether we actually forced runtime suspend
earlier, why couldn't we instead check the runtime PM usage count of
the device?

Only when it's greater than zero, we shall do the forced resume of the
device, otherwise just re-enable runtime PM.

This would have the affect of leaving devices in runtime suspend,
until they really needs to be used again. It would thus decrease the
total system PM resume time.

Do you think this could work?

Kind regards
Uffe

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