Hi On Wed, Feb 12, 2014 at 9:43 PM, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > 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. The "attach" stuff actually sounds doable, but who decides which one to attach? You still need some user-space script during device-plug for that. But to be honest, the simplest way would be a "backlightd" bus-activatable daemon. SetBacklight() then takes a DRM-connector and brightness-value, which the daemon looks up in /sys and sets.. This has the advantage that we can do any fancy matching in user-space. We can provide quirks (maybe even via udev-hwdb) and other helpers for weird setups. Cheers David _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
