<html> <head> <base href="https://bugs.freedesktop.org/" /> </head> <body> <div> <a class="bz_bug_link bz_status_NEEDINFO " title="NEEDINFO --- - [i915 Bayley Bay] Graphics shake/jitter observed when seen on DP monitor" href="https://bugs.freedesktop.org/show_bug.cgi?id=75880#c3">Comment # 3</a> on <a class="bz_bug_link bz_status_NEEDINFO " title="NEEDINFO --- - [i915 Bayley Bay] Graphics shake/jitter observed when seen on DP monitor" href="https://bugs.freedesktop.org/show_bug.cgi?id=75880">bug 75880</a> from <a class="email" href="mailto:achandran@mvista.com" title="arun <achandran@mvista.com>"> arun</a> <pre>Hi, I tried the stable-kernel (<a href="https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/log/?id=refs%2Ftags%2Fv3.12.14&h=linux-3.13.y">https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/log/?id=refs%2Ftags%2Fv3.12.14&h=linux-3.13.y</a>) with ubuntu 13.10; Its behavior is given below. a) When booted with VGA + DP monitor ------------------------------------ Issue exists b) When booted with only DP monitor ----------------------------------- Desktop is stable. So I did a bisect of the kernel and found that the below commit ######################################################## c6cd2ee2d59111a07cd9199564c9bdcb2d11e5cf is the first good commit commit c6cd2ee2d59111a07cd9199564c9bdcb2d11e5cf Author: Jani Nikula <<a href="mailto:jani.nikula@intel.com">jani.nikula@intel.com</a>> Date: Mon Oct 21 10:52:07 2013 +0300 drm/i915/dp: workaround BIOS eDP bpp clamping issue 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 <<a href="mailto:daniel.vetter@ffwll.ch">daniel.vetter@ffwll.ch</a>> 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: <a href="https://bugzilla.kernel.org/show_bug.cgi?id=59841">https://bugzilla.kernel.org/show_bug.cgi?id=59841</a> Bugzilla: <a class="bz_bug_link bz_status_RESOLVED bz_closed" title="RESOLVED FIXED - [ivb regression][bisect] 3.10: i915 blanks eDP panel when CSM is disabled in UEFI" href="show_bug.cgi?id=67950">https://bugs.freedesktop.org/show_bug.cgi?id=67950</a> Tested-by: Ulf Winkelvos <<a href="mailto:ulf@winkelvos.de">ulf@winkelvos.de</a>> Tested-by: jkp <<a href="mailto:jkp@iki.fi">jkp@iki.fi</a>> CC: <a href="mailto:stable@vger.kernel.org">stable@vger.kernel.org</a> Signed-off-by: Jani Nikula <<a href="mailto:jani.nikula@intel.com">jani.nikula@intel.com</a>> Signed-off-by: Daniel Vetter <<a href="mailto:daniel.vetter@ffwll.ch">daniel.vetter@ffwll.ch</a>> ################################################# Fixed this problem in DP only scenario. Commits prior to this on stable linux-3.13.y branch has this issue with only DP monitor connected. Regards, Arun C</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the QA Contact for the bug.</li> <li>You are on the CC list for the bug.</li> </ul> </body> </html>