Am 09.09.2013 19:27, schrieb Frank Schäfer: > Am 05.09.2013 17:57, schrieb Guennadi Liakhovetski: >> On Thu, 5 Sep 2013, Mauro Carvalho Chehab wrote: >>> Rewriting that part of the code would require to test the changes on >>> several hundreds of different devices, and even if you find someone >>> with all those devices, I doubt that he would have enough time to >>> re-test everything. >>> >>> So, either the above unbalance check should be removed, or its behavior >>> should be changed to assume that the devices are ON at probe() time, >>> as it used to be before the async patches. >> Ok, we can certainly do any of the above, but just for understanding - how >> does it actually work now? I mean - ok, I can accept, that the default >> reset state is power on. But the driver then forcedly powers all >> subdevices off upon close() or in the end of initialisation, performed >> during probing - and _never_ explicitly powers them on! That doesn't seem >> right to me. Even if it happens to work. >> >> Further, I grepped em28xx for s_power - only callers have those hooks, I >> didn't find any subdevices with them actually implemented. ov2640 has it >> and it calls soc_camera internal methods, which in the em28xx case also >> end up doing nothing. So, how and which subdevices actually save power >> there and how are they turned back on? >> >> I'll try to look at external subdevice drivers, that are used by em28xx, >> but any hints would be appreciated. > Let's have a look at the commit that introduced the s_power calls: > > commit 622b828ab795580903e79acb33fb44f5c9ce7b0f > Author: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > Date: Mon Oct 5 10:48:17 2009 -0300 > > V4L/DVB (13238): v4l2_subdev: rename tuner s_standby operation to > core s_power > > Upcoming I2C v4l2_subdev drivers need a way to control the subdevice > power state from the core. This use case is already partially covered by > the tuner s_standby operation, but no way to explicitly come back from > the standby state is available. > > Rename the tuner s_standby operation to core s_power, and fix tuner > drivers accordingly. The tuner core will call s_power(0) instead of > s_standby(). No explicit call to s_power(1) is required for tuners as > they are supposed to wake up from standby automatically. > > [mchehab@xxxxxxxxxx: CodingStyle fix] > Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > Signed-off-by: Hans Verkuil <hverkuil@xxxxxxxxx> > Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> > > > > So at least tuners are supposed to wake up automatically. > Yet another reason why these warnings about unbalanced s_power should be > removed. > The problem is, that since this commit ALL subdevices (supporting it) > are put into standby mode, not only the tuners. Hmm... wait. What's s_power supposed to do ? Put the device into stand-by mode or switch power off ? Are we talking about subdevice register operations or can it also call power callbacks in the parent driver (like soc_camera does) ? Regards, Frank > Hopefully, this didn't cause any regressions. > > Regards, > Frank > >> Thanks >> Guennadi >> --- >> Guennadi Liakhovetski, Ph.D. >> Freelance Open-Source Software Developer >> http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
