On Mon, Oct 21, 2013 at 10:52:07AM +0300, Jani Nikula wrote: > This isn't a real fix to the problem, but rather a stopgap measure while > trying to find a proper solution. > > There are several laptops out there that fail to light up the eDP panel > in UEFI boot mode. They seem to be mostly IVB machines, including but > apparently not limited to Dell XPS 13, Asus TX300, Asus UX31A, Asus > UX32VD, Acer Aspire S7. They seem to work in CSM or legacy boot. > > The difference between UEFI and CSM is that the BIOS provides a > different VBT to the kernel. The UEFI VBT typically specifies 18 bpp and > 1.62 GHz link for eDP, while CSM VBT has 24 bpp and 2.7 GHz link. We end > up clamping to 18 bpp in UEFI mode, which we can fit in the 1.62 Ghz > link, and for reasons yet unknown fail to light up the panel. > > Dithering from 24 to 18 bpp itself seems to work; if we use 18 bpp with > 2.7 GHz link, the eDP panel lights up. So essentially this is a link > speed issue, and *not* a bpp clamping issue. > > The bug raised its head since > commit 657445fe8660100ad174600ebfa61536392b7624 > Author: Daniel Vetter <daniel.vetter@xxxxxxxx> > Date: Sat May 4 10:09:18 2013 +0200 > > Revert "drm/i915: revert eDP bpp clamping code changes" > > which started clamping bpp *before* computing the link requirements, and > thus affecting the required bandwidth. Clamping after the computations > kept the link at 2.7 GHz. > > Even though the BIOS tells us to use 18 bpp through the VBT, it happily > boots up at 24 bpp and 2.7 GHz itself! Use this information to > selectively ignore the VBT provided value. > > We can't ignore the VBT eDP bpp altogether, as there are other laptops > that do require the clamping to be used due to EDID reporting higher bpp > than the panel can support. > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=59841 > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67950 > Tested-by: Ulf Winkelvos <ulf@xxxxxxxxxxxx> > Tested-by: jkp <jkp@xxxxxx> > CC: stable@xxxxxxxxxxxxxxx > Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> Both merged to -fixes, thanks for the quick backport. I've added the note about we need the first patch to the commit message and also added the cc: stable tag. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
