On Thu, Feb 13, 2014 at 06:14:04AM +1000, Dave Airlie wrote: > > > > The biggest remaining stumbling block is the backlight API, because opening the > > sysfs files requires root rights. I'll very likely write a little helper for this > > for now, but in the long run it would be good to have a better solution. > > > > While discussion this in the graphics devroom at Fosdem, the general consensus > > seemed to be that the current backlight API is in need of an overhaul anyways. > > > > There are several issues with the current API: > > -there is no reliable way to determine the relation between a backlight > > control in sysfs and the display it controls the backlight off > > -on many laptops we end up with multiple providers of backlight control > > all battling over control of the same backlight controller through various > > firmware interfaces > > -and there is no way to do acl management on it because of sysfs usage > > > > At Fosdem it was suggested to "simply" make the backlight a property of > > the connector in drm/kms and let users control it that way. From an acl pov > > this makes a ton of sense, if a user controls the other display-panel settings, > > then he should be able to control the backlight too. > > > > This also nicely solves the issue of userspace having to figure out which backlight > > control to use for a certain output. > > > > Last this makes it the kernels responsibility to figure out which firmware interface > > (if any) to use and tie that to the connector, rather then just exporting all of > > them, including conflicting ones, and just hoping that userspace will figure things out. > > > > Note that wrt the last point, the kernel is the one which should have all the hardware > > knowledge to do this properly, after all hardware abstraction is one of the tasks of > > the kernel. > > > > I realize moving this more into the kernel, and tying things into drm is in no means > > easy, but it is about time we clean up this mess. > > > > Note that although I'm kicking of this discussion, my focus within the graphics team is > > mostly on input devices, so I'm hoping that someone else will pick things up once we've > > a better idea of how we would like to solve this. > > > > I hate to respond with yeah no, but yeah no, > > http://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&show_html=true&highlight_names=&date=2014-02-04 > http://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&show_html=true&highlight_names=&date=2014-02-05 > > read down that until you see me and tagr talking, read it a few times, > and the follow on chat with dvdhrm. > > The biggest problem with leaving the kernel to pick the correct one, > is the kernel simply never knows which is the > correct one, That could be solved by still allowing userspace to change the connection between the property and the actual backlight device. With the prop approach + atomic modeset you could also do some slightly fancier things like changing the backlight at the same time as doing a modeset or just adjusting some other display related properties. > and you also have to deal with a load of problems like > runtime module deps between very misc modules > or using some kind of notifier mechanism that will turn into a locking > nightmare. This would still be an issue though. I like the idea of the property, but I'm not volunteering to do any of the work. > > I don't mean to dissuade you from trying to "fix" this, but actually > getting a solution upstream is going to require a lot of messing > around. > > Talk to Matthew Garrett, if you haven't talked to him, then you > haven't talked to anyone who understands backlights. > > Dave. > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/dri-devel -- Ville Syrjälä Intel OTC _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
