Hi, On 06/05/2014 04:29 PM, Chris Wilson wrote: > 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. Hmm, interesting, I just checked, and xxx_output_backlight_get in the 2.21.15 driver which is where this is seen indeed reads actual_brightness not just brightness. Where as current master uses backlight not actual_backlight, but some of the reporting users have tried with 2.99.x driver versions and they still had the problem. Still I'll prepare a scratch build for these users using just backlight to see if that helps. >> >> 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. Note that it is read after the framebuffer has been resized and a new mode has been set on "pipe 0 using LVDS1", could this perhaps cause the 0 to be read when using actual_brightness ? Also I've just had a user who has been testing this patch come back to me it does help, but he still has a suspend/resume issue. It seems that some X app / gnome-component is doing the following: 1) DPMS off 2) Read backlight xrandr property -> this will now return 0 3) Set backlight xrandr property value to the value just read, aka 0 4) DPMS on -> "restores" backlight to 0 because of the property set I believe the best way to fix this will be to make xxx_output_get_property("backlight") return backlight_active_level when in DPMS off, rather then calling xxx_output_backlight_get. I'll write a patch doing this tomorrow and ask the user to test (I'm calling it a day for now). If you've a better idea please let me know before I write and submit this patch :) Regards, Hans _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
