[Intel-gfx] [PATCH] drm/i915: Update rules for writing through the LLC with the cpu

[Ville Syrjälä]

On Fri, Aug 09, 2013 at 12:26:45PM +0100, Chris Wilson wrote:
> As mentioned in the previous commit, reads and writes from both the CPU
> and GPU go through the LLC. This gives us coherency between the CPU and
> GPU irrespective of the attribute settings either device sets. We can
> use to avoid having to clflush even uncached memory.
> 
> Except for the scanout.
> 
> The scanout resides within another functional block that does not use
> the LLC but reads directly from main memory. So in order to maintain
> coherency with the scanout, writes to uncached memory must be flushed.
> In order to optimize writes elsewhere, we start tracking whether an
> framebuffer is attached to an object.
> 
> v2: Use pin_display tracking rather than fb_count (to ensure we flush
> cursors as well etc) and only force the clflush along explicit writes to
> the scanout paths (i.e. pin_to_display_plane and pwrite into scanout).
> 
> v3: Force the flush after hitting the slowpath in pwrite, as after
> dropping the lock the object's cache domain may be invalidated. (Ville)
> 
> Based on a patch by Ville Syrjälä.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>

Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

-- 
Ville Syrjälä
Intel OTC