From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: Broken LVDS output at mode changes Date: Thu, 29 Mar 2012 14:51:32 +0200 Message-ID: <20120329125132.GC20275@phenom.ffwll.local> References: <20120329121638.GA20275@phenom.ffwll.local> <1333025081_141778@CP5-2952> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-wg0-f43.google.com (mail-wg0-f43.google.com [74.125.82.43]) by gabe.freedesktop.org (Postfix) with ESMTP id 92F0D9F00C for ; Thu, 29 Mar 2012 05:50:48 -0700 (PDT) Received: by wgbdr12 with SMTP id dr12so1262629wgb.12 for ; Thu, 29 Mar 2012 05:50:47 -0700 (PDT) In-Reply-To: <1333025081_141778@CP5-2952> Content-Disposition: inline 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: Chris Wilson Cc: Takashi Iwai , intel-gfx@lists.freedesktop.org List-Id: intel-gfx@lists.freedesktop.org On Thu, Mar 29, 2012 at 01:44:28PM +0100, Chris Wilson wrote: > On Thu, 29 Mar 2012 14:16:38 +0200, Daniel Vetter wrote: > > On Wed, Mar 28, 2012 at 03:29:04PM +0200, Takashi Iwai wrote: > > > Hi, > > > > > > we've encountered a broken LVDS output on some IVY/SNB machines when > > > the mode is changed (from/to native resolution). When this happens, > > > the whole laptop panel gets half white and half black. This doesn't > > > recover until the LVDS is turned off once. > > > > > > And, there is no signficant difference between working and non-working > > > cases in the register dumps. From the software POV, all looks sane. > > > So, we suspect this is rather specific to some panel hardware. > > > > > > However, through debugging, I found that disabling LVDS at mode change > > > works around the problem. A test patch is attached below. > > > > > > My question now is: can this workaround have any serious drawback? > > > I thought of a longer blank time, but I didn't notice any difference > > > before and after the patch. > > > > > > Or, any other suggestion as a saner fix? > > > > No idea, I'm wondering though whether we should just accept some > > flickering while modesetting unconditionally. Does anyone know what > > Windows does in this case and at least on my work machine here it looks > > like Windows just blanks the screen. I haven't checked with reg dumps > > though how exactly they upscale stuff on lvds. > > > > git blame says that Chris Wilson created the original PCH_SPLIT check. > > Chris, any comments on this? > > It dates back from an earlier commit that presupposes that we can modify > the panel on the fly and avoid the power-cycling delays. > > PP_STATUS: Panel Power On Status [bit 31] > > In conjunction with bits Power Sequence Progress field and Power Cycle > Delay Active, this bit set to a one indicates that the panel is > currently powered up or is currently in the power down sequence and it > is unsafe to change the timing, port, and DPLL registers for the pipe or > transcoder that is assigned to the panel output. > > Guess that rules that out. Takashi, can you respin your patch to just unconditionally switch of the lvds also on PCH_SPLIT platforms then? -Daniel -- Daniel Vetter Mail: daniel@ffwll.ch Mobile: +41 (0)79 365 57 48