drm/xe/mocs: Drop xe_mocs_info_index

The values in the xe_mocs_info_index enum only match old pre-gen12
hardware not supported by the Xe driver.

The only usage of this enum was to set a default value for
info->unused_entries_index, but this is unnecessary since every platform
in the subsequent switch statement sets a proper platform-specific value
(and the XE_MOCS_PTE default doesn't even make sense since the hardware
dropped the "use PAT settings" capability in gen12).

v2:
 - Add a check that unusued_entries_index is non-zero; even for
   platforms where this is a valid table entry, it's never the one we
   want this value assigned to.  (Lucas)
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_mocs.c

@@ -23,30 +23,6 @@ static inline void mocs_dbg(const struct drm_device *dev,
 { /* noop */ }
 #endif
 
-/*
- * MOCS indexes used for GPU surfaces, defining the cacheability of the
- * surface data and the coherency for this data wrt. CPU vs. GPU accesses.
- */
-enum xe_mocs_info_index {
-	/*
-	 * Not cached anywhere, coherency between CPU and GPU accesses is
-	 * guaranteed.
-	 */
-	XE_MOCS_UNCACHED,
-	/*
-	 * Cacheability and coherency controlled by the kernel automatically
-	 * based on the xxxx  IOCTL setting and the current
-	 * usage of the surface (used for display scanout or not).
-	 */
-	XE_MOCS_PTE,
-	/*
-	 * Cached in all GPU caches available on the platform.
-	 * Coherency between CPU and GPU accesses to the surface is not
-	 * guaranteed without extra synchronization.
-	 */
-	XE_MOCS_CACHED,
-};
-
 enum {
 	HAS_GLOBAL_MOCS = BIT(0),
 	HAS_RENDER_L3CC = BIT(1),
@@ -341,7 +317,6 @@ static unsigned int get_mocs_settings(struct xe_device *xe,
 
 	memset(info, 0, sizeof(struct xe_mocs_info));
 
-	info->unused_entries_index = XE_MOCS_PTE;
 	switch (xe->info.platform) {
 	case XE_PVC:
 		info->size = ARRAY_SIZE(pvc_mocs_desc);
@@ -395,6 +370,16 @@ static unsigned int get_mocs_settings(struct xe_device *xe,
 		return 0;
 	}
 
+	/*
+	 * Index 0 is a reserved/unused table entry on most platforms, but
+	 * even on those where it does represent a legitimate MOCS entry, it
+	 * never represents the "most cached, least coherent" behavior we want
+	 * to populate undefined table rows with.  So if unused_entries_index
+	 * is still 0 at this point, we'll assume that it was omitted by
+	 * mistake in the switch statement above.
+	 */
+	XE_WARN_ON(info->unused_entries_index == 0);
+
 	if (XE_WARN_ON(info->size > info->n_entries))
 		return 0;
 
@@ -406,9 +391,8 @@ static unsigned int get_mocs_settings(struct xe_device *xe,
 }
 
 /*
- * Get control_value from MOCS entry taking into account when it's not used
- * then if unused_entries_index is non-zero then its value will be returned
- * otherwise XE_MOCS_PTE's value is returned in this case.
+ * Get control_value from MOCS entry.  If the table entry is not defined, the
+ * settings from unused_entries_index will be returned.
  */
 static u32 get_entry_control(const struct xe_mocs_info *info,
 			     unsigned int index)