Re: [PATCH 2/3] usb: misc: ljca: set small runtime autosuspend delay

[Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>]

On Mon, Nov 04, 2024 at 02:50:31PM +0100, Hans de Goede wrote:
> Hi,
> 
> On 4-Nov-24 9:50 AM, Stanislaw Gruszka wrote:
> > On some Lenovo platforms, the patch workarounds problems with ov2740
> > sensor initialization, which manifest themself like below:
> > 
> > [    4.540476] ov2740 i2c-INT3474:01: error -EIO: failed to find sensor
> > [    4.542066] ov2740 i2c-INT3474:01: probe with driver ov2740 failed with error -5
> > 
> > or
> > 
> > [    7.742633] ov2740 i2c-INT3474:01: chip id mismatch: 2740 != 0
> > [    7.742638] ov2740 i2c-INT3474:01: error -ENXIO: failed to find sensor
> > 
> > and also by random failures of video stream start.
> > 
> > Issue can be reproduced by this script:
> > 
> > n=0
> > k=0
> > while [ $n -lt 50 ] ; do
> > 	sudo modprobe -r ov2740
> > 	sleep `expr $RANDOM % 5`
> > 	sudo modprobe ov2740
> > 	if media-ctl -p  | grep -q ov2740 ; then
> > 		let k++
> > 	fi
> > 	let n++
> > done
> > echo Success rate $k/$n
> > 
> > Without the patch, success rate is approximately 15 or 50 tries.
> > With the patch it does not fail.
> > 
> > This problem is some hardware or firmware malfunction, that can not be
> > easy debug and fix. While setting small autosuspend delay is not perfect
> > workaround as user can configure it to any value, it will prevent
> > the failures by default.
> > 
> > Additionally setting small autosuspend delay should have positive effect
> > on power consumption as for most ljca workloads device is used for just
> > a few milliseconds flowed by long periods of at least 100ms of inactivity
> > (usually more).
> > 
> > Fixes: acd6199f195d ("usb: Add support for Intel LJCA device")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
> 
> Thank you so much for looking into this and fixing it!
> 
> Patch looks good to me:
> 
> Reviewed-by: Hans de Goede <hdegoede@redhat.com>
> 
> I have also given this a test run on a "ThinkPad X1 Yoga Gen 8" and
> everything there works at least as well as before:
> 
> Tested-by: Hans de Goede <hdegoede@redhat.com> # ThinkPad X1 Yoga Gen 8, ov2740
> 
> Regards,
> 
> Hans
> 
> p.s.
> 
> I take it from the commit message that you have no clear idea what exactly is
> happening in the failure case ?

Yes, that's correct. We have only some suspicions, but none of them
was confirmed.

Regards
Stanislaw