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

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Message-ID: <CAPDyKFr5bPCcDmgQNeXCHJNoPLKD7BLVL8m8eh1sh1CXMbNDRA@mail.gmail.com>
Date:	Fri, 22 Apr 2016 09:15:05 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	"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 21 April 2016 at 23:07, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> Hi Rafael,
>
> On Thursday 21 Apr 2016 23:02:06 Rafael J. Wysocki wrote:
>> On Thu, Apr 21, 2016 at 10:57 PM, Laurent Pinchart wrote:
>> > 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. :-)
>
> Let's see what we can do in a reasonable time frame. We could decide to merge
> this patch as a temporary fix until the genpd rework is complete.

Subsystems/driver that uses pm_runtime_force_suspend|resume() don't
necessarily need to have their devices attached to a genpd. In such
cases, $subject patch will be an improvement by itself.

Me personally would rather skip the intermediate step you propose, as
I prefer to properly change genpd with what is needed. Moreover, I am
already working on that so it shouldn't take too long before I can
post some patches.

Kind regards
Uffe