On 07/18/2012 08:15 AM, Paul Berry wrote:
> On Gen6, multisampled null render targets don't seem to work
> properly--they cause the GPU to hang. So, as a workaround, we render
> into a dummy color buffer.
>
> Fortunately this situation (multisampled rendering without a color
> buffer) is rare, and we don't have to waste too much memory, because
> we can give the workaround buffer a very small pitch.
>
> Fixes piglit test "EXT_framebuffer_multisample/no-color {2,4}
> depth-computed *" on Gen6.
> - surf[0] = (BRW_SURFACE_NULL << BRW_SURFACE_TYPE_SHIFT |
> + if (fb->Visual.samples > 0) {
> + /* On Gen6, null render targets seem to cause GPU hangs when
> + * multisampling. So work around this problem by rendering into dummy
> + * color buffer.
> + *
> + * To decrease the amount of memory needed by the workaround buffer, we
> + * set its pitch to 128 bytes (the width of a Y tile). This means that
> + * the amount of memory needed for the workaround buffer is
> + * (width_in_tiles + height_in_tiles - 1) tiles.
It took me several minutes to see why this was the lower bound of needed memory.
Reviewed-by: Chad Versace <chad.vers...@linux.intel.com>
I'm off to the dentist now, so I might not be able today to respond to your
comments on my msaa patch series.
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