Re: [RFT][PATCH] iio: hid-sensor-trigger: Fix the race with user space powering up sensors

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 11 Aug 2017 16:04:30 +0200
Bastien Nocera <hadess@hadess.net> wrote:

> Woot!
> 
> On Thu, 2017-08-10 at 16:24 -0700, Srinivas Pandruvada wrote:
> > It has been reported for a while that with iio-sensor-proxy service the
> > rotation only works after one suspend/resume cycle. This required a wait
> > in the systemd unit file to avoid race. I found a Yoga 900 where I could
> > reproduce this.
> > 
> > The problem scenerio is:
> > - During sensor driver init, enable run time PM and also set a
> >   auto-suspend for 3 seconds.
> > 	This result in one runtime resume. But there is a check to avoid
> > a powerup in this sequence, but rpm is active
> > - User space iio-sensor-proxy tries to power up the sensor. Since rpm is
> >   active it will simply return. But sensors were not actually
> > powered up in the prior sequence, so actaully the sensors will not work
> > - After 3 seconds the auto suspend kicks
> > 
> > If we add a wait in systemd service file to fire iio-sensor-proxy after
> > 3 seconds, then now everything will work as the runtime resume will
> > actually powerup the sensor as this is a user request.
> > 
> > To avoid this:
> > - Remove the check to match user requested state, this will cause a
> >   brief powerup, but if the iio-sensor-proxy starts immediately it will
> > still work as the sensors are ON.
> > - Also move the autosuspend delay to place when user requested turn off
> >   of sensors, like after user finished raw read or buffer disable
> > 
> > Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>  
> 
> Tested-by: Bastien Nocera <hadess@hadess.net>
> 
> I'm still chasing a couple of bugs in the user-space side of things
> caused by the removal of the timeout.
> 
> Thanks!
Is it worth me sitting on this for a week or so to see if it deals with
all the reported issues around this?

Or are you happy that the test set you have is sufficient to verify it?

Definitely good to put this one to bed finally! 

Jonathan