[Intel-gfx] [PATCH 10/15] drm/i915: check the power well when capturing error state

[Daniel Vetter]

On Wed, Mar 06, 2013 at 08:03:17PM -0300, Paulo Zanoni wrote:
> From: Paulo Zanoni <paulo.r.zanoni at intel.com>
> 
> This solves many "unclaimed register" messages when the power well is
> down and we get a GPU hang.
> 
> Also print the power well register and each pipe's CPU transcoder on
> the error state to allow proper interpratation of the registers. And
> kzalloc the error state structure since we may not read some of the
> registers (to avoid the "unclaimed register" messages).
> 
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>

Ok, I've thought some more about all and you're all going to hate me.

Essentially I don't like that we have rather invasive patches for a minor
feature with _very_ delicate limits as to what hits the debug yelling and
what doesn't. Furthermore the debug feature isn't that clear-cut since
interrupts get in the way (and we cant fix that since that would also
disable underrun interrupts, which we want). And the audio driver also
randomly inteferes.

Now where it's justified that a register doesn't exist I don't mind
merging the patches - it's always good to have accurate documentation of
what's really used by the hw. But for debug features I'm really uneasy
with runtime checks, since it might very well be that those are wrong.

Hence I vote for a I915_READ_NOCHECK to avoid all this madness. This one
will never check for errors, but silently clear them after a read. Note
that we don't need a I915_WRITE_NOCHECK, and imo that's good since writing
random crap could indeed be a serious bug.

So I'll punt on this patch since imo it's too messy for future
maintenance. Same for the other debug patches (e.g. the assert_pipe_enabled
check).

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch