From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Wilson Subject: Re: [PATCH] drm/i915: rip out early dp port write for gm45/ilk Date: Thu, 13 Sep 2012 11:10:14 +0100 Message-ID: <6c3329$61f23h@orsmga002.jf.intel.com> References: <1347485049-19003-1-git-send-email-daniel.vetter@ffwll.ch> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by gabe.freedesktop.org (Postfix) with ESMTP id E6EC5A0AED for ; Thu, 13 Sep 2012 03:10:29 -0700 (PDT) In-Reply-To: <1347485049-19003-1-git-send-email-daniel.vetter@ffwll.ch> 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: Intel Graphics Development Cc: Daniel Vetter List-Id: intel-gfx@lists.freedesktop.org On Wed, 12 Sep 2012 23:24:09 +0200, Daniel Vetter wrote: > It's bogus. > > If I've followed the history of this piece of code correctly, i.e. the > initial register write with the following vblank wait, this goes all > the way back to the original enabling of DP support in > > commit a4fc5ed69817c73e32571ad7837bb707f9890009 > Author: Keith Packard > Date: Tue Apr 7 16:16:42 2009 -0700 > > drm/i915: Add Display Port support > > Unfortunately it seems to be nothing more than glorified duct-tape and > sometimes actively harmful. Adam Jackson noticed this for CPT > platforms with > > commit e85194641bec56179dcf5e1704ce5c6bf30340c6 > Author: Adam Jackson > Date: Thu Jul 21 17:48:38 2011 -0400 > > drm/i915/dp: Don't turn CPT DP ports on too early > > Unfortunately this kept the code around for ilk and gm45. > > The specific failure case I'm seeing here is that after a dpms off/on > cycle we have the bits from the last link training (hopefully > successful link training) set in intel_dp->DP. This is requiered so > that complete_link_train can enable the port with the right tuning > values. > > Unfortunately writing these again to the disabled port at dpms on time > kills the port somehow until it's disabled - dp link training fails in > an endless loop without this patch on my mobile ilk and gm45. > > Cc: Chris Wilson > Signed-Off-by: Daniel Vetter Works for me, only time will time if I no longer get the occasional failure in link training, but it definitely fixes the issue with dpms off. Tested-by: Chris Wilson Probably https://bugs.freedesktop.org/show_bug.cgi?id=51493 -Chris -- Chris Wilson, Intel Open Source Technology Centre