[Mesa-dev] SandyBridge issue likely related to fast color clears using meta operations

[Samuel Iglesias Gonsálvez]

Adding Kristian in Cc.

Sam

On Tue, 2014-09-02 at 18:16 +0200, Samuel Iglesias Gonsálvez wrote:
> Hello,
> 
> Two weeks ago, Iago and myself sent a batch of patches that added
> geometry shader support for SandyBridge [0].
> 
> Recently, we rebased our patches against master [1] and found
> that some things are not working properly any more. Particularly, we
> have plenty of cases where we only get a black screen when using a
> geometry shader, and in these cases it seems as if some outputs of the
> geometry shader got "lost" by the time they become inputs in the
> fragment shader (some input varyings in the fragment shader that come
> from the outputs of the geometry seem to be zeroed). The values we
> output in the geometry shader are correct though, since they are
> correctly captured by transform feedback.
> 
> A bisect shows that the commit that introduced this problem is
> 2f28a0dc231 i965: Implement fast color clears using meta operations [2].
> 
> Reverting this commit fixes the problem for us. The revert also fixes
> piglit's bin/gl-3.2-layered-rendering-clear-color* tests in SandyBridge
> [3].
> 
> So the question is whether the commit mentioned above introduces a
> regression that should be fixed somewhere or if our code needs to be
> updated to adapt to changes introduced by that commit in some way.
> 
> Best regards,
> 
> Sam
> 
> [0]
> http://lists.freedesktop.org/archives/mesa-dev/2014-August/065692.html
> 
> [1]
> https://github.com/samuelig/mesa/tree/gs-support-snb-for-submission-02092014
> 
> [2]
> commit 2f28a0dc23165123cf1e8b5942acad37878edd8a
> Author: Kristian Høgsberg <krh at bitplanet.net>
> Date:   Mon Jul 7 16:44:58 2014 -0700
> 
>     i965: Implement fast color clears using meta operations
>     
>     This patch uses the infrastructure put in place by previous patches
>     to implement fast color clears and replicated color clears in terms 
>     of meta operations.
>     
>     This works all the way back to gen7 where fast clear was introduced 
>     and adds support for fast clear on gen8.  It replaces the blorp path
>     completely and improves on a few cases.  Layered clears are now done
>     using instanced rendering and multiple render-target clears use a
>     MRT shader with rep16 writes.
>     
>     Signed-off-by: Kristian Høgsberg <krh at bitplanet.net>
>     Acked-by: Kenneth Graunke <kenneth at whitecape.org>
> 
> [3]
> http://people.igalia.com/siglesias/mesa/all-gs-patches-v2/changes.html
> _______________________________________________
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