freedreno: Add common VRS helpers

These will be used by ir3 and turnip.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36892>

src/freedreno/common/freedreno_vrs.h

@@ -0,0 +1,107 @@
+/*
+ * Copyright © 2025 Valve Corporation
+ * SPDX-License-Identifier: MIT
+ */
+
+#ifndef __FREEDRENO_VRS_H__
+#define __FREEDRENO_VRS_H__
+
+#include "util/macros.h"
+
+/* HW values for shading rate. This matches D3D12_SHADING_RATE. The value is
+ * encoded as (width_log2 << 2) | height_log2, but a width or height of 8 is
+ * not supported.  Vulkan and GL shading rate values are specified as
+ * (height_log2 << 2) | width_log2, and are translated to this via lookup
+ * tables in the last pre-rasterization shader (for per-primitive shading
+ * rate) and GRAS (for attachment-based shading rate).
+ */
+
+enum fd_shading_rate {
+   FD_SHADING_RATE_1X1 = 0,
+   FD_SHADING_RATE_1X2 = 1,
+   FD_SHADING_RATE_1X4 = 2,
+   FD_SHADING_RATE_2X1 = 4,
+   FD_SHADING_RATE_2X2 = 5,
+   FD_SHADING_RATE_2X4 = 6,
+   FD_SHADING_RATE_4X1 = 8,
+   FD_SHADING_RATE_4X2 = 9,
+   FD_SHADING_RATE_4X4 = 10,
+   FD_SHADING_RATE_INVALID = 11, /* used in shader LUT */
+};
+
+#define VK_SHADING_RATE(wlog2, hlog2) (((hlog2) << 2) | (wlog2))
+#define VK_SHADING_RATE_INVALID 11
+
+static const uint32_t vk_to_hw_shading_rate_lut[] = {
+   [VK_SHADING_RATE(0, 0)] = FD_SHADING_RATE_1X1,
+   [VK_SHADING_RATE(1, 0)] = FD_SHADING_RATE_2X1,
+   [VK_SHADING_RATE(2, 0)] = FD_SHADING_RATE_4X1,
+   [VK_SHADING_RATE(3, 0)] = FD_SHADING_RATE_INVALID,
+
+   [VK_SHADING_RATE(0, 1)] = FD_SHADING_RATE_1X2,
+   [VK_SHADING_RATE(1, 1)] = FD_SHADING_RATE_2X2,
+   [VK_SHADING_RATE(2, 1)] = FD_SHADING_RATE_4X2,
+   [VK_SHADING_RATE(3, 1)] = FD_SHADING_RATE_INVALID,
+
+   [VK_SHADING_RATE(0, 2)] = FD_SHADING_RATE_1X4,
+   [VK_SHADING_RATE(1, 2)] = FD_SHADING_RATE_2X4,
+   [VK_SHADING_RATE(2, 2)] = FD_SHADING_RATE_4X4,
+   [VK_SHADING_RATE(3, 2)] = FD_SHADING_RATE_INVALID,
+
+   [VK_SHADING_RATE(0, 3)] = FD_SHADING_RATE_INVALID,
+   [VK_SHADING_RATE(1, 3)] = FD_SHADING_RATE_INVALID,
+   [VK_SHADING_RATE(2, 3)] = FD_SHADING_RATE_INVALID,
+   [VK_SHADING_RATE(3, 3)] = FD_SHADING_RATE_INVALID,
+};
+
+/* The value provided to the FS is the HW value which must be translated back
+ * to the VK/GL value via this lookup table.
+ */
+
+static const uint32_t hw_to_vk_shading_rate_lut[] = {
+   [FD_SHADING_RATE_1X1] = VK_SHADING_RATE(0, 0),
+   [FD_SHADING_RATE_1X2] = VK_SHADING_RATE(0, 1),
+   [FD_SHADING_RATE_1X4] = VK_SHADING_RATE(0, 2),
+   [3] = VK_SHADING_RATE_INVALID,
+
+   [FD_SHADING_RATE_2X1] = VK_SHADING_RATE(1, 0),
+   [FD_SHADING_RATE_2X2] = VK_SHADING_RATE(1, 1),
+   [FD_SHADING_RATE_2X4] = VK_SHADING_RATE(1, 2),
+   [7] = VK_SHADING_RATE_INVALID,
+
+   [FD_SHADING_RATE_4X1] = VK_SHADING_RATE(2, 0),
+   [FD_SHADING_RATE_4X2] = VK_SHADING_RATE(2, 1),
+   [FD_SHADING_RATE_4X4] = VK_SHADING_RATE(2, 2),
+   [11] = VK_SHADING_RATE_INVALID,
+
+   [12] = VK_SHADING_RATE_INVALID,
+   [13] = VK_SHADING_RATE_INVALID,
+   [14] = VK_SHADING_RATE_INVALID,
+   [15] = VK_SHADING_RATE_INVALID,
+};
+
+/* The GRAS lookup table is an array of 4-bit values packed into 32-bit
+ * registers. Calculate the value to put in the given register.
+ */
+
+static ALWAYS_INLINE uint32_t
+fd_gras_shading_rate_lut(unsigned index)
+{
+   if (index / 8 >= ARRAY_SIZE(vk_to_hw_shading_rate_lut))
+      return 0;
+
+   uint32_t ret = 0;
+   for (unsigned i = 0; i < 8; i++) {
+      uint32_t rate = vk_to_hw_shading_rate_lut[index * 8 + i];
+      /* For some reason the blob avoids writing INVALID in the GRAS lookup
+       * table, unlike the shader lookup table. Follow it here.
+       */
+      if (rate == FD_SHADING_RATE_INVALID)
+         rate = 0;
+      ret |= rate << (4 * i);
+   }
+
+   return ret;
+}
+
+#endif

src/freedreno/common/meson.build

@@ -26,6 +26,7 @@ libfreedreno_common = static_library(
     'freedreno_uuid.c',
     'freedreno_uuid.h',
     'freedreno_guardband.h',
+    'freedreno_vrs.h',
     freedreno_devices_h,
     sha1_h,
     'redump.h'