[Mesa-dev] [PATCH 2/2] i965 gen6: Implement rasterizer discard.

[Kenneth Graunke]

On 12/14/2011 11:59 AM, Paul Berry wrote:
> This patch enables rasterizer discard functionality (a part of
> transform feedback) in Gen6, by generating an alternate GS program
> when rasterizer discard is active.  Instead of forwarding vertices
> down the pipeline, the alternate GS program uses a URB Write message
> to deallocate the URB entry that was allocated by FF sync and
> terminate the thread.
> 
> Note: parts of the Sandy Bridge PRM seem to imply that we could do
> this more efficiently, by clearing the GEN6_GS_RENDERING_ENABLE bit,
> and not allocating a URB entry at all.  However, it's not clear how we
> are supposed to terminate the thread if we do that.  Volume 2 part 1,
> section 4.5.4, says "GS threads must terminate by sending a URB_WRITE
> message with the EOT and Complete bits set.", and my experiments so
> far confirm that.
> ---
> 
> This patch needs to be applied on top of the series "[PATCH 0/8] i965
> gen6: Initial implementation of transform feedback.", which is still
> under review on the mailing list.

Assuming the dirty bit gets sorted out,
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>