[Intel-gfx] Redo a modeset on link training failure

[Manasi Navare]

Hi Ville,

I have implemented the code that we discussed where if the link training
fails, it would validate the modes on the new constraints and call
an atomic helper like drm_atomic_helper_connector_modeset() to redo
a modeset for the same mode. The two patches for this implemnetation is
are:

http://paste.ubuntu.com/23357104/
http://paste.ubuntu.com/23357105/

With this I can successfully trigger the modeset and retrain the link
at lower link rate. But I am getting a warning during intel_audio_codec_enable()
in intel_enable_ddi() during the commit phase on SKL.
Following is the dmesg log:

http://paste.ubuntu.com/23357075/

After further looking at it, I see that this calls drm_select_eld() function
that throws a warning if the mode_config mutex and modeset locks are held.
If I remove those WARN_ONs from there, I can get rid of this warning and
everything works smoothly.

Do you know if those WARN_ONs are required because these locks would be grabbed
when we are in modeset.

Regards
Manasi