On Fri, 14 Sep 2012 14:12:19 +0100, David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: > On Fri, 2012-09-14 at 14:09 +0100, Grant Likely wrote: > > On Fri, Sep 14, 2012 at 2:01 PM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > > > On Fri, 14 Sep 2012 13:57:06 +0100, Grant Likely <grant.likely@xxxxxxxxxxxx> wrote: > > >> Some platforms (for instance MacbookPros) have custom backlight drivers > > >> and don't use the integrated i915 backlight control. This patch adds a > > >> quirk to disable registering the intel backlight when unused on a > > >> platform. > > >> > > >> Tested on MacbookPro8,3. Without this patch both the intel_backlight and > > >> gmux_backlight devices get registered and userspace doesn't know which > > >> it should use. > > > > > > Userspace is informed throught the backlight/type property. > > > > Perhaps, but userspace (Ubuntu) isn't doing anything with it, and it > > still remains that it makes no sense whatsoever to register a > > backlight device that doesn't exist. > > Indeed. Userspace (well, gnome-settings-daemon) will use the backlight > provided by X, in preference to anything it finds > in /sys/class/backlight. So if the Intel one is present (and thus > exposed via X) then userspace will never bother with comparing types and > choosing the sanest backlight to use. > > See https://bugzilla.redhat.com/show_bug.cgi?id=752595 And if you look at that bug, it starts off by complaining that a workaround is required in order to use the intel_backlight. By the time you hit the issue with apple_gmux, the upstream ddx already carried the fix for a couple of months and even had it in a release. And more recently we took a patch to allow the user to override which backlight is preferred to handle the case of a broken platform/firmware interface being selected instead of intel_backlight. Userspace is indeed trying to do the right thing with the information provided by the kernel. apple_gmux is not the only device with a phantom PWM BLC, which is why the default preference is to use the platform/firmware provided backlight interface, if any. -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
