[Intel-gfx] [PATCH] drm/i915: rip out early dp port write for gm45/ilk

[Chris Wilson]

On Wed, 12 Sep 2012 23:24:09 +0200, Daniel Vetter <daniel.vetter at ffwll.ch> 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 <keithp at keithp.com>
> 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 <ajax at redhat.com>
> 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 <chris at chris-wilson.co.uk>
> Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

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 <chris at chris-wilson.co.uk>
Probably https://bugs.freedesktop.org/show_bug.cgi?id=51493
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre