Makes sense.
Reviewed-by: Marek Olšák <marek.ol...@amd.com>
Marek
On Wed, Feb 22, 2017 at 7:59 PM, Nicolai Hähnle <nhaeh...@gmail.com> wrote:
> From: Nicolai Hähnle <nicolai.haeh...@amd.com>
>
> 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-sta...@lists.freedesktop.org
> ---
> src/mesa/state_tracker/st_atom.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/src/mesa/state_tracker/st_atom.c
> b/src/mesa/state_tracker/st_atom.c
> index 65ac517..9e1137e 100644
> --- a/src/mesa/state_tracker/st_atom.c
> +++ b/src/mesa/state_tracker/st_atom.c
> @@ -181,21 +181,29 @@ void st_validate_state( struct st_context *st, enum
> st_pipeline pipeline )
> struct gl_program *new_cp = ctx->ComputeProgram._Current;
>
> if (new_cp != &old_cp->Base) {
> if (old_cp)
> st->dirty |= old_cp->affected_states;
> assert(new_cp);
> st->dirty |= st_compute_program(new_cp)->affected_states;
> }
>
> 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;
> }
>
> default:
> unreachable("Invalid pipeline specified");
> }
>
> dirty = st->dirty & pipeline_mask;
> if (!dirty)
> return;
> --
> 2.9.3
>
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