linux-kernel - Re: [PATCH] PM: sleep: core: Avoid setting power.must

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Message-ID: <YQ1SRbBrcKl2Vt9f@kroah.com>
Date:   Fri, 6 Aug 2021 17:16:21 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     psodagud@...eaurora.org
Cc:     rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM: sleep: core: Avoid setting power.must_resume to false

On Fri, Aug 06, 2021 at 08:07:08AM -0700, psodagud@...eaurora.org wrote:
> On 2021-08-03 10:16, Greg KH wrote:
> > On Mon, Jul 26, 2021 at 08:24:34AM -0700, Prasad Sodagudi wrote:
> > > There are variables(power.may_skip_resume and dev->power.must_resume)
> > > and DPM_FLAG_MAY_SKIP_RESUME flags to control the resume of devices
> > > after
> > > a system wide suspend transition.
> > > 
> > > Setting the DPM_FLAG_MAY_SKIP_RESUME flag means that the driver allows
> > > its "noirq" and "early" resume callbacks to be skipped if the device
> > > can be left in suspend after a system-wide transition into the working
> > > state. PM core determines that the driver's "noirq" and "early" resume
> > > callbacks should be skipped or not with dev_pm_skip_resume()
> > > function by
> > > checking power.may_skip_resume variable.
> > > 
> > > power.must_resume variable is getting set to false in
> > > __device_suspend()
> > > function without checking device's DPM_FLAG_MAY_SKIP_RESUME and
> > > dev->power.usage_count variables. This is leading to failure to call
> > > resume handler for some of the devices suspended in early suspend
> > > phase.
> > > So check device's DPM_FLAG_MAY_SKIP_RESUME flag before
> > > setting power.must_resume variable.
> > > 
> > > Signed-off-by: Prasad Sodagudi <psodagud@...eaurora.org>
> > > ---
> > >  drivers/base/power/main.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > > index d568772..8eebc4d 100644
> > > --- a/drivers/base/power/main.c
> > > +++ b/drivers/base/power/main.c
> > > @@ -1642,7 +1642,11 @@ static int __device_suspend(struct device
> > > *dev, pm_message_t state, bool async)
> > >  	}
> > > 
> > >  	dev->power.may_skip_resume = true;
> > > -	dev->power.must_resume = false;
> > > +	if ((atomic_read(&dev->power.usage_count) <= 1) &&
> > > +			(dev_pm_test_driver_flags(dev, DPM_FLAG_MAY_SKIP_RESUME)))
> > 
> > What is preventing that atomic value from changing _right_ after you
> > just read this?
> > 
> > and very odd indentation, checkpatch didn't complain about this?
> Sure. I will fix indentation problem once Rafael reviewed this patch.

Neither of us can take this as-is, so why wait?