[Mesa-dev] [PATCH 3/3] panfrost: Assign varying buffers dynamically

[Alyssa Rosenzweig]

Rather than hardcoding certain varying buffer indices "by convention",
work it out at draw time. This added flexibility is needed for
futureproofing and will be enable streamout.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
---
 src/gallium/drivers/panfrost/pan_assemble.c |  6 ---
 src/gallium/drivers/panfrost/pan_varyings.c | 53 +++++++++------------
 2 files changed, 23 insertions(+), 36 deletions(-)

diff --git a/src/gallium/drivers/panfrost/pan_assemble.c b/src/gallium/drivers/panfrost/pan_assemble.c
index 15f77585a25..c56881c0a69 100644
--- a/src/gallium/drivers/panfrost/pan_assemble.c
+++ b/src/gallium/drivers/panfrost/pan_assemble.c
@@ -138,28 +138,22 @@ panfrost_shader_compile(
                 /* Check for special cases, otherwise assume general varying */
 
                 if (location == VARYING_SLOT_POS) {
-                        v.index = 1;
                         v.format = MALI_VARYING_POS;
                 } else if (location == VARYING_SLOT_PSIZ) {
-                        v.index = 2;
                         v.format = MALI_R16F;
                         v.swizzle = default_vec1_swizzle;
 
                         state->writes_point_size = true;
                 } else if (location == VARYING_SLOT_PNTC) {
-                        v.index = 3;
                         v.format = MALI_RG16F;
                         v.swizzle = default_vec2_swizzle;
 
                         state->reads_point_coord = true;
                 } else if (location == VARYING_SLOT_FACE) {
-                        v.index = 4;
                         v.format = MALI_R32I;
                         v.swizzle = default_vec1_swizzle;
 
                         state->reads_face = true;
-                } else {
-                        v.index = 0;
                 }
 
                 state->varyings[i] = v;
diff --git a/src/gallium/drivers/panfrost/pan_varyings.c b/src/gallium/drivers/panfrost/pan_varyings.c
index b918d1426c4..b4ed512917a 100644
--- a/src/gallium/drivers/panfrost/pan_varyings.c
+++ b/src/gallium/drivers/panfrost/pan_varyings.c
@@ -60,6 +60,20 @@ panfrost_emit_front_face(union mali_attr *slot)
 
 /* Given a shader and buffer indices, link varying metadata together */
 
+static bool
+is_special_varying(gl_varying_slot loc)
+{
+        switch (loc) {
+        case VARYING_SLOT_POS:
+        case VARYING_SLOT_PSIZ:
+        case VARYING_SLOT_PNTC:
+        case VARYING_SLOT_FACE:
+                return true;
+        default:
+                return false;
+        }
+}
+
 static void
 panfrost_emit_varying_meta(
                 void *outptr, struct panfrost_shader_state *ss,
@@ -115,19 +129,9 @@ panfrost_emit_varying_descriptor(
         struct panfrost_transfer trans = panfrost_allocate_transient(ctx,
                                          vs_size + fs_size);
 
-        /*
-         * Assign ->src_offset now that we know about all the general purpose
-         * varyings that will be used by the fragment and vertex shaders.
-         */
         for (unsigned i = 0; i < vs->tripipe->varying_count; i++) {
-                /*
-                 * General purpose varyings have ->index set to 0, skip other
-                 * entries.
-                 */
-                if (vs->varyings[i].index)
-                        continue;
-
-                vs->varyings[i].src_offset = 16 * (num_gen_varyings++);
+                if (!is_special_varying(vs->varyings_loc[i]))
+                        vs->varyings[i].src_offset = 16 * (num_gen_varyings++);
         }
 
         for (unsigned i = 0; i < fs->tripipe->varying_count; i++) {
@@ -177,15 +181,14 @@ panfrost_emit_varying_descriptor(
         memcpy(trans.cpu, vs->varyings, vs_size);
         memcpy(trans.cpu + vs_size, fs->varyings, fs_size);
 
-        /* Buffer indices must be in this order per our convention */
         union mali_attr varyings[PIPE_MAX_ATTRIBS];
-        unsigned idx = 0;
 
+        unsigned idx = 0;
         signed general = idx++;
         signed gl_Position = idx++;
-        signed gl_PointSize = (vs->writes_point_size || fs->reads_point_coord || fs->reads_face) ? (idx++) : -1;
-        signed gl_PointCoord = (fs->reads_point_coord || fs->reads_face) ? (idx++) : -1;
-        signed gl_FrontFacing = (fs->reads_face) ? (idx++) : -1;
+        signed gl_PointSize = vs->writes_point_size ? (idx++) : -1;
+        signed gl_PointCoord = fs->reads_point_coord ? (idx++) : -1;
+        signed gl_FrontFacing = fs->reads_face ? (idx++) : -1;
 
         panfrost_emit_varyings(ctx, &varyings[general], num_gen_varyings * 16,
                                vertex_count);
@@ -196,26 +199,16 @@ panfrost_emit_varying_descriptor(
                                        sizeof(float) * 4, vertex_count);
 
 
-        if (vs->writes_point_size || fs->reads_point_coord) {
-                /* fp16 vec1 gl_PointSize */
+        if (vs->writes_point_size)
                 ctx->payloads[PIPE_SHADER_FRAGMENT].primitive_size.pointer =
                         panfrost_emit_varyings(ctx, &varyings[gl_PointSize],
                                                2, vertex_count);
-        } else if (fs->reads_face) {
-                /* Dummy to advance index */
-                ++idx;
-        }
 
-        if (fs->reads_point_coord) {
-                /* Special descriptor */
+        if (fs->reads_point_coord)
                 panfrost_emit_point_coord(&varyings[gl_PointCoord]);
-        } else if (fs->reads_face) {
-                ++idx;
-        }
 
-        if (fs->reads_face) {
+        if (fs->reads_face)
                 panfrost_emit_front_face(&varyings[gl_FrontFacing]);
-        }
 
         /* Let's go ahead and link varying meta to the buffer in question, now
          * that that information is available */
-- 
2.20.1