[Intel-gfx] [PATCH] drm/i915: don't double-restore ARB mode bits for kms

[Daniel Vetter]

On Thu, Jan 16, 2014 at 5:54 PM, Paulo Zanoni <przanoni at gmail.com> wrote:
> 2014/1/16 Daniel Vetter <daniel.vetter at ffwll.ch>:
>> Our init_clock_gating functions and related code should already take
>> care of this. And if they don't we'd better know.
>
> For both registers, I see functions applying specific workarounds, but
> they only do the read-write-modify through _MASKED_BIT_ENABLE(). I
> don't see anybody explicitly fully initializing the registers
> anywhere. So we go with whatever the BIOS gives us at boot + our
> changes to a few specific registers. At resume, we don't know so far
> what we'll get, so I fear this patch may in fact cause a regression.

That's part of the risk of it, but fixing those is a simple matter of
comparing register dumps. These two bits here are one of the very few
holdouts we have that depend upon the register save/restore code, and
I want to remove them. Since thus far this was a really good way to
hide random bugs.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch