st/mesa: inform the driver of framebuffer changes before compute dispatches

Even though compute shaders cannot access the framebuffer, there is a
synchronization issue when a compute dispatch accesses a texture that
was previously bound and drawn to as a framebuffer.

Section 9.3 (Feedback Loops Between Textures and the Framebuffer) of
the OpenGL 4.5 spec rather implicitly clarifies that undefined behavior
results if the texture is still attached to the currently bound
framebuffer. However, the feedback loop is broken when the application
changes the framebuffer binding before a compute dispatch, and the
state tracker needs to let the driver known about this.

Fixes GL45-CTS.compute_shader.pipeline-post-fs on SI family Radeons.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Marek Olšák <marek.olsak@amd.com>

diff --git a/src/mesa/state_tracker/st_atom.c b/src/mesa/state_tracker/st_atom.c
index 4bef3423b07870b49373f20b9bcb8bad81e6dd19..abbbd4d45a3c887f12cfcc3f36038807a20c9784 100644 (file)
--- a/src/mesa/state_tracker/st_atom.c
+++ b/src/mesa/state_tracker/st_atom.c
@@ -198,7 +198,15 @@ void st_validate_state( struct st_context *st, enum st_pipeline pipeline )
       }
 
       st->compute_shader_may_be_dirty = false;
-      pipeline_mask = ST_PIPELINE_COMPUTE_STATE_MASK;
+
+      /*
+       * We add the ST_NEW_FB_STATE bit here as well, because glBindFramebuffer
+       * acts as a barrier that breaks feedback loops between the framebuffer
+       * and textures bound to the framebuffer, even when those textures are
+       * accessed by compute shaders; so we must inform the driver of new
+       * framebuffer state.
+       */
+      pipeline_mask = ST_PIPELINE_COMPUTE_STATE_MASK | ST_NEW_FB_STATE;
       break;
    }