drm/i915/overlay: Allocate physical registers from stolen
Given that we are now reasonably confident in our ability to detect and
reserve the stolen memory (physical memory reserved for graphics by the
BIOS) for ourselves on most machines, we can put it to use. In this
case, we need a page to hold the overlay registers.
On an i915g running MythTv, H Buus noticed that
commit 6a2c4232ece145d8b5a8f95f767bd6d0d2d2f2bb
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Tue Nov 4 04:51:40 2014 -0800
drm/i915: Make the physical object coherent with GTT
introduced stuttering into his video playback. After discarding the
likely suspect of it being the physical cursor updates, we were left
with the use of the phys object for the overlay. And lo, if we
completely avoid using the phys object (allocated just once on module
load!) by switching to stolen memory, the stuttering goes away.
For lack of a better explanation, claim victory and kill two birds with
one stone.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107600
Fixes: 6a2c4232ece1 ("drm/i915: Make the physical object coherent with GTT")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180906190144.1272-1-chris@chris-wilson.co.uk
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