freedreno/ir3: cleanup driver-param stuff

Add 'enum ir3_driver_param' to track driver-param slots, and a
create_driver_param() helper to avoid having the knowledge about
where driver params are placed in const regs spread throughout
the code as we add additional driver-params.

Signed-off-by: Rob Clark <robclark@freedesktop.org>

src/gallium/drivers/freedreno/ir3/ir3_compiler_nir.c

@@ -261,13 +261,26 @@ compile_init(struct ir3_compiler *compiler,
 
 	so->first_driver_param = so->first_immediate = ctx->s->num_uniforms;
 
-	/* one (vec4) slot for vertex id base: */
-	if (so->type == SHADER_VERTEX)
-		so->first_immediate++;
+	/* Layout of constant registers:
+	 *
+	 *    num_uniform * vec4  -  user consts
+	 *    4 * vec4            -  UBO addresses
+	 *    if (vertex shader) {
+	 *        1 * vec4        -  driver params (IR3_DP_*)
+	 *    }
+	 *
+	 * TODO this could be made more dynamic, to at least skip sections
+	 * that we don't need..
+	 */
 
 	/* reserve 4 (vec4) slots for ubo base addresses: */
 	so->first_immediate += 4;
 
+	if (so->type == SHADER_VERTEX) {
+		/* one (vec4) slot for driver params (see ir3_driver_param): */
+		so->first_immediate++;
+	}
+
 	return ctx;
 }
 
@@ -811,6 +824,14 @@ create_frag_face(struct ir3_compile *ctx, unsigned comp)
 	}
 }
 
+static struct ir3_instruction *
+create_driver_param(struct ir3_compile *ctx, enum ir3_driver_param dp)
+{
+	/* first four vec4 sysval's reserved for UBOs: */
+	unsigned r = regid(ctx->so->first_driver_param + 4, dp);
+	return create_uniform(ctx, r);
+}
+
 /* helper for instructions that produce multiple consecutive scalar
  * outputs which need to have a split/fanout meta instruction inserted
  */
@@ -1415,9 +1436,7 @@ emit_intrinisic(struct ir3_compile *ctx, nir_intrinsic_instr *intr)
 		break;
 	case nir_intrinsic_load_base_vertex:
 		if (!ctx->basevertex) {
-			/* first four vec4 sysval's reserved for UBOs: */
-			unsigned r = regid(ctx->so->first_driver_param + 4, 0);
-			ctx->basevertex = create_uniform(ctx, r);
+			ctx->basevertex = create_driver_param(ctx, IR3_DP_VTXID_BASE);
 			add_sysval_input(ctx, TGSI_SEMANTIC_BASEVERTEX,
 					ctx->basevertex);
 		}

src/gallium/drivers/freedreno/ir3/ir3_shader.c

@@ -548,10 +548,7 @@ ir3_emit_consts(struct ir3_shader_variant *v, struct fd_ringbuffer *ring,
 		uint32_t offset = v->first_driver_param + 4;  /* driver params after UBOs */
 		if (v->constlen >= offset) {
 			uint32_t vertex_params[4] = {
-				info->indexed ? info->index_bias : info->start,
-				0,
-				0,
-				0
+				[IR3_DP_VTXID_BASE] = info->indexed ? info->index_bias : info->start,
 			};
 
 			fd_wfi(ctx, ring);

src/gallium/drivers/freedreno/ir3/ir3_shader.h

@@ -34,6 +34,11 @@
 #include "ir3.h"
 #include "disasm.h"
 
+/* driver param indices: */
+enum ir3_driver_param {
+	IR3_DP_VTXID_BASE = 0,
+};
+
 /* internal semantic used for passing vtxcnt to vertex shader to
  * implement transform feedback:
  */