gallium: add get_compute_state_subgroup_size

This will be required by drivers supporting multiple subgroup sizes with
a given CSO to properly implement OpenCL subgroups.

Signed-off-by: Karol Herbst <git@karolherbst.de>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22893>

docs/gallium/context.rst

@@ -888,6 +888,16 @@ get_compute_state_info
 This function allows frontends to query kernel information defined inside
 ``pipe_compute_state_object_info``.
 
+.. _get_compute_state_subgroup_size:
+
+get_compute_state_subgroup_size
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+This function returns the choosen subgroup size when `launch_grid` is
+called with the given block size. This doesn't need to be implemented when
+only one size is reported through ``PIPE_COMPUTE_CAP_SUBGROUP_SIZES`` or
+``pipe_compute_state_object_info::simd_sizes``.
+
 Mipmap generation
 ^^^^^^^^^^^^^^^^^
 

src/gallium/include/pipe/p_context.h

@@ -946,6 +946,9 @@ struct pipe_context {
    void (*get_compute_state_info)(struct pipe_context *, void *,
                                   struct pipe_compute_state_object_info *);
 
+   uint32_t (*get_compute_state_subgroup_size)(struct pipe_context *, void *,
+                                               const uint32_t block[3]);
+
    /**
     * Bind an array of shader resources that will be used by the
     * compute program.  Any resources that were previously bound to