Hi Hans, On Fri, Oct 20, 2017 at 01:56:48PM +0200, Hans Verkuil wrote: > On 19/10/17 16:53, Sakari Ailus wrote: > > Hi Harald and Hans, > > > > On Thu, Oct 19, 2017 at 03:09:15PM +0200, Harald Dankworth wrote: > >> Find the major and minor numbers of the device. Check if the > >> file /dev/dev/char/major:minor/uevent contains "DEVNAME=v4l-subdev". /sys/dev/... > >> If so, the device is a sub-device. > >> > >> Signed-off-by: Harald Dankworth <hardankw@xxxxxxxxx> > >> Reviewed-by: Hans Verkuil <hansverk@xxxxxxxxx> > > > > I wonder if this is the best way to obtain the information. I thought there > > was an intent to add something to sysfs that wasn't based on device names. > > This also hardcodes the sysfs path. > > This is what we discussed on irc some time ago. And if /sys is mounted somewhere > else, then you have bigger problems :-) I remember the discussion but my recollection of the conclusion is slightly different. :-) Besides, sysfs could be still mounted elsewhere. > > The device name in /sys comes from the driver and isn't changed by udev rules. > So we can use it to determine if it is a subdev or not. > > > Would udev provide anything useful in this respect? > > Not all embedded systems use udev. I'd rather not depend on it, at least not for > this utility. > > The alternative to this is to add a QUERYCAP-like ioctl for subdevs, but my > proposal for that has been repeatedly shot down. Here's a new argument for that: in order to make sub-devices proper V4L2 devices there should be QUERYCAP support. It'd be the same IOCTL and the same argument struct. > > In the meantime we need *something* so you can use v4l2-ctl to query/get/set > controls and the EDID for HDMI receivers (Tim Harvey needs this). > > I would like to merge this soon. It can always be changed if we switch to another > better method. I agree, this won't break anything and can be improved later on without affecting anything else. Acked-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> -- Sakari Ailus e-mail: sakari.ailus@xxxxxx
