panfrost: Add note about preloaded varyings

There's a magic bit in preload_regs which controls this. It doesn't
appear to be supported on G71 but it is on G52. I'd guess G72 supports
it too but I don't have a way to check this.

Needless to say, we'll need a quirks database for this.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4061>

diff --git a/src/panfrost/include/panfrost-job.h b/src/panfrost/include/panfrost-job.h
index 1e67c150aa8115ba8734cab6ad07a0fc56fe02f4..4f1edeb8453efd71a18f22cbf4f8bae31a1b18a1 100644 (file)
--- a/src/panfrost/include/panfrost-job.h
+++ b/src/panfrost/include/panfrost-job.h
@@ -601,6 +601,11 @@ struct mali_shader_meta {
                          * - R61 : gl_SampleMaskIn and gl_SampleID, used by
                          *   varying interpolation.
                          * - R62 : unknown (bit always unset).
+                         *
+                         * Later GPUs (starting with Mali-G52?) support
+                         * preloading float varyings into r0-r7. This is
+                         * indicated by setting 0x40. There is no distinction
+                         * here between 1 varying and 2.
                          */
                         u32 preload_regs : 8;
                         /* In units of 8 bytes or 64 bits, since the