iris: Add fast-clear restriction for 8bpp surfaces

For 8bpp surfaces on TGL, prevent LOD1+ from being fast-cleared. This
will be relevant once ISL starts allowing CCS for 8bpp surfaces with
more than 2 miplevels. I verified the problem behind this restriction
with a modified version of the fbo-clearmipmap piglit test.

Reviewed-by: Sagar Ghuge <sagar.ghuge@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7085>

src/gallium/drivers/iris/iris_clear.c

@@ -114,6 +114,23 @@ can_fast_clear_color(struct iris_context *ice,
    if (!iris_is_color_fast_clear_compatible(ice, res->surf.format, color))
       return false;
 
+   /* The RENDER_SURFACE_STATE page for TGL says:
+    *
+    *   For an 8 bpp surface with NUM_MULTISAMPLES = 1, Surface Width not
+    *   multiple of 64 pixels and more than 1 mip level in the view, Fast Clear
+    *   is not supported when AUX_CCS_E is set in this field.
+    *
+    * The granularity of a fast-clear is one CCS element. For an 8 bpp primary
+    * surface, this maps to 32px x 4rows. Due to the surface layout parameters,
+    * if LOD0's width isn't a multiple of 64px, LOD1 and LOD2+ will share CCS
+    * elements. Assuming LOD2 exists, don't fast-clear any level above LOD0
+    * to avoid stomping on other LODs.
+    */
+   if (level > 0 && util_format_get_blocksizebits(p_res->format) == 8 &&
+       res->aux.usage == ISL_AUX_USAGE_GEN12_CCS_E && p_res->width0 % 64) {
+      return false;
+   }
+
    return true;
 }