[Intel-gfx] [Regression] "drm/i915: Implement display w/a #1143" breaks HDMI on ASUS GL552VW

[Vivi, Rodrigo]

Art, any comment here?

I just checked and the  W/a 1143 is implemented as described, but it is
failing HDMI on this hybrid system.

> On Aug 12, 2020, at 9:07 PM, Kai-Heng Feng <kai.heng.feng at canonical.com> wrote:
> 
> Hi,
> 
> There's a regression reported that HDMI output stops working after os upgrade:
> https://bugs.launchpad.net/bugs/1871721
> 
> Here's the bisect result:
> 0519c102f5285476d7868a387bdb6c58385e4074 is the first bad commit
> commit 0519c102f5285476d7868a387bdb6c58385e4074
> Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Date:   Mon Jan 22 19:41:31 2018 +0200
> 
>    drm/i915: Implement display w/a #1143
> 
>    Apparently SKL/KBL/CFL need some manual help to get the
>    programmed HDMI vswing to stick. Implement the relevant
>    workaround (display w/a #1143).
> 
>    Note that the relevant chicken bits live in a transcoder register
>    even though the bits affect a specific DDI port rather than a
>    specific transcoder. Hence we must pick the correct transcoder
>    register instance based on the port rather than based on the
>    cpu_transcoder.
> 
>    Also note that for completeness I included support for DDI A/E
>    in the code even though we never have HDMI on those ports.
> 
>    v2: CFL needs the w/a as well (Rodrigo and Art)
> 
>    Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>    Cc: Art Runyan <arthur.j.runyan at intel.com>
>    Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
>    Link: https://patchwork.freedesktop.org/patch/msgid/20180122174131.28046-1-ville.syrjala@linux.intel.com
>    Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> 
> 
> dmesg from drm-tip with drm.debug=0xe can be found here:
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1871721/comments/64
> 
> Kai-Heng