On Tue, Jun 27, 2017 at 10:29:33PM +0000, Pandiyan, Dhinakaran wrote: > > > > On Tue, 2017-06-27 at 16:23 +0300, David Weinehall wrote: > > On Mon, Jun 26, 2017 at 05:18:19PM +0300, David Weinehall wrote: > > > On Thu, Jun 22, 2017 at 12:03:39PM -0700, Puthikorn Voravootivat wrote: > > > > This patch adds option to enable dynamic backlight for eDP > > > > panel that supports this feature via DPCD register and > > > > set minimum / maximum brightness to 0% and 100% of the > > > > normal brightness. > > > > > > This patch causes a regression on my ThinkPad X1 Carbon Gen 4; > > > with enable_dbc = true the backlight stays off; setting i915.enable_dbc=0 > > > on boot makes things work properly again. > > > > Some more testing indicates that while i915.enable_dbc=0 solves the > > initial issue of backlight not coming on, it's not enough--after > > suspend/resume the backlight stays off. > > > > Passing i915.enable_dpcd_backlight=0 seems to work both for the initial > > case of backlight not coming on at boot, and the issue with backlight > > not coming on after suspend/resume. > > > > So: > > > > DBC:1, DPCD: -1: blank screen on boot > > DBC:0, DPCD: -1: screen OK on boot, blank after suspend/resume > > DBC:1, DPCD: 0: screen OK on boot, screen OK after suspend/resume > > DBC:0, DPCD: 0: screen OK on boot, screen OK after suspend/resume > > > > So it seems that at least for the ThinkPad X1 Carbon Gen 4 (possibly > > limited to the 2560x1440 model) DPCD backlight isn't supported. > > > > Hi David, > > Thanks for the bug report. It's come a bit sooner than I expected > though. > > We shouldn't be enabling DPCD backlight control if the panel does not > support it. I'd like to look at the dmesg with drm.debug=0xE. We debug > log the panel capabilities early during boot and that will be useful. > Can you also provide the output of i915_dpcd in debugfs for the eDP > connector? > > I guess it makes sense to file an FDO and attach the logs there. https://bugs.freedesktop.org/show_bug.cgi?id=101619 Kind regards, David _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
