Hi, On 02/12/2014 11:26 PM, David Herrmann wrote: > 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. This sounds like a good idea, note that at-least gnome already has something similar in the form of the (one-shot, not daemon) gsd-backlight-helper which also has some code to try and figure out what is the right backlight class device to use. Interestingly enough the xf86-video-intel driver does this on its own using somewhat more complex logic to find the right backlight class device to use, and then exporting this as a property on the connector in Xrandr. So a first rough idea of how this would work / a plan would be: 1) We have a bus-activated backlightd running as root 2) This can be asked for backlight properties on a certain drm/kms connector 3) If there actually is a backlight for the connector, it can also be used to change the backlight brightness 4) The xserver will get some helper functions which drivers can call to create a backlight property on xrandr connectors 5) In the long run gsd-backlight-helper and the xf86-video-intel backlight code can be removed Note there also is a step: 0) Get xf86-video-intel backlight code to work without root in some way for now Regards, Hans _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
