intel: Add and use isl_get_sampler_clear_field_offset

Add and use a function which documents the sampler's behavior around
fast-clears on gfx11-12.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30520>

src/gallium/drivers/iris/iris_resolve.c

@@ -1163,19 +1163,13 @@ iris_resource_prepare_texture(struct iris_context *ice,
       clear_supported = false;
    }
 
-   /* On gfx11+, the sampler reads clear values stored in pixel form.  The
-    * location the sampler reads from is dependent on the bits-per-channel of
-    * the format.  Specifically, a pixel is read from the Raw Clear Color
-    * fields if the format is 32bpc.  Otherwise, it's read from the Converted
-    * Clear Color fields.  To avoid modifying the clear color, disable it if
-    * the new format points the sampler to an incompatible location.
-    *
-    * Note: although hardware looks at the bits-per-channel of the format, we
-    * only need to check the red channel's size here.  In the scope of formats
-    * supporting fast-clears, all 32bpc formats have 32-bit red channels and
-    * vice-versa.
+   /* With indirect clear colors, the sampler reads clear values stored in
+    * pixel form.  The location the sampler reads from is dependent on the
+    * bits-per-channel of the format.  Disable support for clear colors if the
+    * new format points the sampler to an incompatible location.  See
+    * isl_get_sampler_clear_field_offset() for more information.
     */
-   if (devinfo->ver >= 11 &&
+   if (res->aux.clear_color_bo &&
        isl_format_get_layout(res->surf.format)->channels.r.bits != 32 &&
        isl_format_get_layout(view_format)->channels.r.bits == 32) {
       clear_supported = false;

src/intel/blorp/blorp_blit.c

@@ -2973,24 +2973,14 @@ blorp_copy(struct blorp_batch *batch,
 
    if (isl_aux_usage_has_fast_clears(params.src.aux_usage) &&
        isl_dev->ss.clear_color_state_size > 0) {
-      /* For 32bpc formats, the sampler fetches the raw clear color dwords
-       * used for rendering instead of the converted pixel dwords typically
-       * used for sampling. The CLEAR_COLOR struct page documents this for
-       * 128bpp formats, but not for 32bpp and 64bpp formats.
-       *
-       * Note that although the sampler doesn't use the converted clear color
-       * field with 32bpc formats, the Clear Color Conversion hardware feature
-       * still occurs when the format sizes are less than 128bpp.
-       *
-       * The sampler changing its clear color fetching location can be a
-       * problem in some cases, but we won't run into them here. When using an
-       * indirect clear color, we won't create 32bpc views of non-32bpc
-       * surfaces (and vice-versa).
+      /* Depending on the format, the sampler may change the location from
+       * which it fetches the clear color. This can be a problem in some
+       * cases, so make sure that the view format won't change the location.
        */
-      const struct isl_format_layout *src_view_fmtl =
-         isl_format_get_layout(params.src.view.format);
-      assert((src_fmtl->channels.r.bits == 32) ==
-             (src_view_fmtl->channels.r.bits == 32));
+      ASSERTED enum isl_format src_view_fmt = params.src.view.format;
+      ASSERTED enum isl_format src_surf_fmt = params.src.surf.format;
+      assert(isl_get_sampler_clear_field_offset(devinfo, src_view_fmt) ==
+             isl_get_sampler_clear_field_offset(devinfo, src_surf_fmt));
    }
 
    if (params.src.view.format != params.dst.view.format) {

src/intel/isl/isl.c

@@ -459,6 +459,33 @@ isl_device_get_sample_counts(const struct isl_device *dev)
    }
 }
 
+uint64_t
+isl_get_sampler_clear_field_offset(const struct intel_device_info *devinfo,
+                                   enum isl_format format)
+{
+   assert(devinfo->ver == 11 || devinfo->ver == 12);
+
+   /* For 32bpc formats, the sampler fetches the raw clear color dwords
+    * used for rendering instead of the converted pixel dwords typically
+    * used for sampling. The CLEAR_COLOR struct page documents this for
+    * 128bpp formats, but not for 32bpp and 64bpp formats.
+    *
+    * Note that although the sampler doesn't use the converted clear color
+    * field with 32bpc formats, the hardware will still convert the clear
+    * color to a pixel when the surface format size is less than 128bpp.
+    */
+   if (isl_format_get_layout(format)->channels.r.bits == 32)
+      return 0;
+
+   /* According to Wa_2201730850, the gfx120 sampler reads the
+    * U24_X8-formatted pixel from the first raw clear color dword.
+    */
+   if (devinfo->verx10 == 120 && format == ISL_FORMAT_R24_UNORM_X8_TYPELESS)
+      return 0;
+
+   return 16;
+}
+
 static uint32_t
 isl_get_miptail_base_row(enum isl_tiling tiling)
 {

src/intel/isl/isl.h

@@ -1984,6 +1984,14 @@ isl_device_init(struct isl_device *dev,
 isl_sample_count_mask_t ATTRIBUTE_CONST
 isl_device_get_sample_counts(const struct isl_device *dev);
 
+/**
+ * :returns: The offset of the field within CLEAR_COLOR from which the sampler
+ *           fetches the clear color.
+ */
+uint64_t
+isl_get_sampler_clear_field_offset(const struct intel_device_info *devinfo,
+                                   enum isl_format format);
+
 /**
  * :returns: The isl_format_layout for the given isl_format
  */