On Thu, Jun 05, 2014 at 05:01:23PM +0300, Jani Nikula wrote: > On Thu, 05 Jun 2014, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > > We've several reports from users where the backlight comes up turned off > > on starting X, when using video.use_native_backlight=1 (true dmi quirks, will > > be the default for 3.16), in combination with having an external display > > plugged in: > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1032978 > > https://bugzilla.redhat.com/show_bug.cgi?id=1103806 > > > > This seems to be caused by /sys/class/backlight/intel_backlight/brightness > > reading back 0 when re-initializing the outputs. Unlike > > /sys/class/backlight/acpi_video0/brightness which is used without the > > video.use_native_backlight=1 param, which keeps returning the value from before > > > > Here is an excerpt from Xorg.log when this happens: > > > > [28225]: (II) intel(0): resizing framebuffer to 3286x1080 > > [28225]: (II) intel(0): switch to mode 1366x768@59.8 on pipe 0 using LVDS1, position (0, 0), rotation normal > > [28225]: (II) intel(0): switch to mode 1920x1080@60.0 on pipe 0 using HDMI2, position (1366, 0), rotation normal > > [28225]: (II) intel(0): DPMS off mode 3, saved backlight level 0 > > ^^^ This is an extra debug line I added, mode == the mode parameter to > > xxx_output_dpms_backlight, saved backlight level is the value of > > backlight_active_level after the xxx_output_backlight_get call. > > > > Note how backlight_active_level becomes 0 here. > > > > [28225]: (II) intel(0): switch to mode 1366x768@59.8 on pipe 1 using LVDS1, position (0, 0), rotation normal > > [28225]: (II) intel(0): DPMS on mode 0, setting backlight to 0 > > > > And here we restore the backlight to backlight_active_level which now is 0. > > > > This commit fixes this by not reading back the backlight setting from the > > kernel on DPMS off. > > I'm not at all familiar with the code base you're changing, and I'm just > speculating here, but this seems a little odd. > > My guess is that the sna_output_backlight_get and/or > intel_output_backlight_get functions read the actual_brightness sysfs > file, which reads back the value from hardware. This is the contract for > backlight class device. The acpi video implementation returns the cached > value if there's no BQC or BCQ method. > > I think perhaps either the current brightness should be read before > switching off the output. It is read before we switch off the CRTC (and thus the output). So where it is getting the zero from is a puzzle - it should be the current state of the hardware, ergo what the user set by some other path. -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
