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

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Message-ID: <1683904.kdfvDOmCDR@avalon>
Date:	Fri, 22 Apr 2016 00:07:36 +0300
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
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

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.

-- 
Regards,

Laurent Pinchart