Mesa (main): panfrost: Set overdraw_alpha[01] flags

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Module: Mesa
Branch: main
Commit: e7a7679b9a77bd4b4300c19bc6b3365756f03c5b
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=e7a7679b9a77bd4b4300c19bc6b3365756f03c5b

Author: Alyssa Rosenzweig <alyssa at collabora.com>
Date:   Fri May 27 08:46:46 2022 -0400

panfrost: Set overdraw_alpha[01] flags

These basically correspond to the alpha_zero_nop and alpha_one_store flags we
already compute and set. Except those flags don't exist on Valhall, so these
need to be used instead (on Bifrost, in addition .. unclear why the duplication
on Bifrost).

Set these flags when we can. Ostensibly this is for performance (neglible
improvement on glmark2 score), but mostly I want to get us using the hardware
optimally.

Signed-off-by: Alyssa Rosenzweig <alyssa at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16748>

---

 src/gallium/drivers/panfrost/pan_cmdstream.c | 40 ++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/src/gallium/drivers/panfrost/pan_cmdstream.c b/src/gallium/drivers/panfrost/pan_cmdstream.c
index f9b89e0e29f..35fbb0af0fc 100644
--- a/src/gallium/drivers/panfrost/pan_cmdstream.c
+++ b/src/gallium/drivers/panfrost/pan_cmdstream.c
@@ -315,6 +315,32 @@ pack_blend_constant(enum pipe_format format, float cons)
         return unorm << (16 - chan_size);
 }
 
+/*
+ * Determine whether to set the respective overdraw alpha flag.
+ *
+ * The overdraw alpha=1 flag should be set when alpha=1 implies full overdraw,
+ * equivalently, all enabled render targets have alpha_one_store set. Likewise,
+ * overdraw alpha=0 should be set when alpha=0 implies no overdraw,
+ * equivalently, all enabled render targets have alpha_zero_nop set.
+ */
+static bool
+panfrost_overdraw_alpha(const struct panfrost_context *ctx, bool zero)
+{
+        const struct panfrost_blend_state *so = ctx->blend;
+
+        for (unsigned i = 0; i < ctx->pipe_framebuffer.nr_cbufs; ++i) {
+                const struct pan_blend_info info = so->info[i];
+
+                bool enabled = ctx->pipe_framebuffer.cbufs[i] && info.no_colour;
+                bool flag = zero ? info.alpha_zero_nop : info.alpha_one_store;
+
+                if (enabled && !flag)
+                        return false;
+        }
+
+        return true;
+}
+
 static void
 panfrost_emit_blend(struct panfrost_batch *batch, void *rts, mali_ptr *blend_shaders)
 {
@@ -468,6 +494,10 @@ pan_merge_empty_fs(struct mali_renderer_state_packed *rsd)
                 cfg.properties.allow_forward_pixel_to_kill = true;
                 cfg.properties.allow_forward_pixel_to_be_killed = true;
                 cfg.properties.zs_update_operation = MALI_PIXEL_KILL_STRONG_EARLY;
+
+                /* Alpha isn't written so these are vacuous */
+                cfg.multisample_misc.overdraw_alpha0 = true;
+                cfg.multisample_misc.overdraw_alpha1 = true;
 #else
                 cfg.shader.shader = 0x1;
                 cfg.properties.work_register_count = 1;
@@ -580,6 +610,9 @@ panfrost_prepare_fs_state(struct panfrost_context *ctx,
                  */
                 cfg.properties.point_sprite_coord_origin_max_y =
                         (rast->sprite_coord_mode == PIPE_SPRITE_COORD_LOWER_LEFT);
+
+                cfg.multisample_misc.overdraw_alpha0 = panfrost_overdraw_alpha(ctx, 0);
+                cfg.multisample_misc.overdraw_alpha1 = panfrost_overdraw_alpha(ctx, 1);
 #endif
 
                 cfg.stencil_mask_misc.alpha_to_coverage = alpha_to_coverage;
@@ -3283,6 +3316,9 @@ panfrost_emit_draw(void *out,
                         cfg.blend_count = MAX2(batch->key.nr_cbufs, 1);
                         cfg.alpha_to_coverage = ctx->blend->base.alpha_to_coverage;
 
+                        cfg.overdraw_alpha0 = panfrost_overdraw_alpha(ctx, 0);
+                        cfg.overdraw_alpha1 = panfrost_overdraw_alpha(ctx, 1);
+
                         panfrost_emit_shader(batch, &cfg.shader, PIPE_SHADER_FRAGMENT,
                                              batch->rsd[PIPE_SHADER_FRAGMENT],
                                              batch->tls.gpu);
@@ -3302,6 +3338,10 @@ panfrost_emit_draw(void *out,
 
                         /* No shader => no shader side effects */
                         cfg.allow_forward_pixel_to_be_killed = true;
+
+                        /* Alpha isn't written so these are vacuous */
+                        cfg.overdraw_alpha0 = true;
+                        cfg.overdraw_alpha1 = true;
                 }
 #else
                 cfg.position = pos;