linux-kernel - Re: [PATCH v2] PM / Runtime: Only force-resume device if it has been force-suspended

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Date:	Thu, 21 Apr 2016 23:02:06 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Kevin Hilman <khilman@...nel.org>,
	linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v2] PM / Runtime: Only force-resume device if it has been force-suspended

On Thu, Apr 21, 2016 at 10:57 PM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> Hi Rafael,
>
> On Thursday 21 Apr 2016 21:52:56 Rafael J. Wysocki wrote:
>> On Thursday, April 21, 2016 02:52:55 AM Laurent Pinchart 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
>> > manage 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, regardless
>> > 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
>> > unconditionally 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>
>> > Reviewed-by: Kevin Hilman <khilman@...libre.com>
>>
>> Ulf, any comments?
>
> Ulf has proposed a different approach in "[PATCH] PM / Runtime: Defer resuming
> of the device in pm_runtime_force_resume()". I agree that using usage_count is
> better than introducing a new state flag in struct dev_pm_info, with a caveat:
> it doesn't work properly :-). We would have to fix genpd first, as commented
> in a reply to Ulf's patch.

OK, thanks!

Since I'd prefer to avoid adding more state flags too, I'll let you
guys noodle around this for a while more. :-)