[Intel-gfx] [PATCH 1/2] drm/i915: Remove use of the autoreported ringbuffer HEAD position

[Eric Anholt]

On Wed,  8 Feb 2012 13:34:13 +0000, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> This is a revert of 6aa56062eaba67adfb247cded244fd877329588d.
> 
> This was originally introduced to workaround reads of the ringbuffer
> registers returning 0 on SandyBridge causing hangs due to ringbuffer
> overflow. The root cause here was reads through the GT powerwell require
> the forcewake dance, something we only learnt of later. Now it appears
> that reading the reported head position from the HWS is returning
> garbage, leading once again to hangs.

Tested-by: Eric Anholt <eric at anholt.net>

(on top of de67cba65944f26c0f147035bd62e30c5f456b96, this fixes
rendering failures and GPU hangs on gen7).
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