[Intel-gfx] [PATCH] drm/i915: Add support for resetting the SO write pointers on gen7.

[Kenneth Graunke]

On 12/29/2011 05:52 PM, Eric Anholt wrote:
> These registers are automatically incremented by the hardware during
> transform feedback to track where the next streamed vertex output
> should go.  Unlike the previous generation, which had a packet for
> setting the corresponding registers to a defined value, gen7 only has
> MI_LOAD_REGISTER_IMM to do so.  That's a secure packet (since it loads
> an arbitrary register), so we need to do it from the kernel, and it
> needs to be settable atomically with the batchbuffer execution so that
> two clients doing transform feedback don't stomp on each others'
> state.
> 
> Instead of building a more complicated interface involcing setting the
> registers to a specific value, just set them to 0 when asked and
> userland can tweak its pointers accordingly.
> 
> Signed-off-by: Eric Anholt <eric at anholt.net>

Looks great!

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>