Created attachment 75313 [details] [review]
Fixes on the Workaround

Hi Jerome, this is the patch I actually used.
I had already done what you said and also removed a couple of left shifts you
had added upon reading the low words.
The results are still the same, though.

Right now I'm tracing it by going through the code between the call to
DAC1OutputControl on radeon_atom_encoder_dpms_avivo and the call to
DPEncoderService on either radeon_dp_encoder_service or radeon_dp_link_train
and instrumenting it, not sure which one yet, but I'm guessing the first. This
is to make sure the driver is not doing anything else that could be going wrong
in between calls, because after that DAC1OutputControl call, everything is
still fine, it's somewhere in between those calls that the adapter goes to
hell.

Another thing that I'd like to ask is, you suggested me to "make sure the pipes
are off". I've looked through the registers looking for something to get DAC
state or disable them, and have not found it. As far as I can tell, your patch
would already make sure we're not doing improper access, but are there any more
interesting registers I should be looking into as well?

Thanks