From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: [PATCH for 3.12/-fixes 2/2] drm/i915/dp: workaround BIOS eDP bpp clamping issue Date: Mon, 21 Oct 2013 10:06:20 +0200 Message-ID: <20131021080620.GF4830@phenom.ffwll.local> References: <1381932378-14890-2-git-send-email-jani.nikula@intel.com> <1382341927-19401-1-git-send-email-jani.nikula@intel.com> <1382341927-19401-2-git-send-email-jani.nikula@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ee0-f54.google.com (mail-ee0-f54.google.com [74.125.83.54]) by gabe.freedesktop.org (Postfix) with ESMTP id E2A5AE65DE for ; Mon, 21 Oct 2013 01:05:59 -0700 (PDT) Received: by mail-ee0-f54.google.com with SMTP id e53so3368042eek.41 for ; Mon, 21 Oct 2013 01:05:59 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1382341927-19401-2-git-send-email-jani.nikula@intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org To: Jani Nikula Cc: intel-gfx@lists.freedesktop.org List-Id: intel-gfx@lists.freedesktop.org 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 > 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 > Tested-by: jkp > CC: stable@vger.kernel.org > Signed-off-by: Jani Nikula 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