[Intel-gfx] [PATCH] drm/i915: wait for a vblank to pass after tv detect

[Chris Wilson]

On Tue, 22 May 2012 21:25:08 +0200, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> Otherwise the hw will get confused and result in a black screen.
> 
> This regression has been most likely introduce in
> 
> commit 974b93315b2213b74a42a87e8a9d4fc8c0dbe90c
> Author: Chris Wilson <chris at chris-wilson.co.uk>
> Date:   Sun Sep 5 00:44:20 2010 +0100
> 
>     drm/i915/tv: Poll for DAC state change
> 
> That commit replace the first msleep(20) with a busy-loop, but failed
> to keep the 2nd msleep around. Later on we've replaced all these
> msleep(20) by proper vblanks.
> 
> For reference also see the commit in xf86-video-intel:
> 
> commit 1142be53eb8d2ee8a9b60ace5d49f0ba27332275
> Author: Jesse Barnes <jbarnes at hobbes.lan>
> Date:   Mon Jun 9 08:52:59 2008 -0700
> 
>     Fix TV programming:  add vblank wait after TV_CTL writes
> 
>     Fxies FDO bug #14000; we need to wait for vblank after
>     writing TV_CTL or following "DPMS on" calls may not actually enable the output.
> 
> Launchpad: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/763688
> Reported-and-Tested-by: Robert Lowery <rglowery at exemail.com.au>
> Cc: Rodrigo Vivi <rodrigo.vivi at gmail.com>
> Cc: stable at kernel.org
> Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Still lacking an accurate explanation for why the wait is required, both
in the changelog and code.  Especially the code.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre