[PATCH] uapi/drm/drm_fourcc.h: Note on platform specificity for format modifiers

[Mika Kahola]

Make an additional note on DRM format modifiers for x and y tiling. These
format modifiers are defined for BDW+ platforms and therefore definition
is not valid for older gens. This is due to address swizzling for tiled
surfaces is no longer used. For newer platforms main memory controller has
a more effective address swizzling algorithm.

Signed-off-by: Mika Kahola <mika.kahola at intel.com>
---
 include/uapi/drm/drm_fourcc.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
index 8bc0b31597d8..3e56c24cabb6 100644
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/drm/drm_fourcc.h
@@ -356,7 +356,8 @@ extern "C" {
  *
  * This format is highly platforms specific and not useful for cross-driver
  * sharing. It exists since on a given platform it does uniquely identify the
- * layout in a simple way for i915-specific userspace.
+ * layout in a simple way for i915-specific userspace.  The format is
+ * ill-defined for platforms older than BDW.
  */
 #define I915_FORMAT_MOD_X_TILED	fourcc_mod_code(INTEL, 1)
 
@@ -371,7 +372,8 @@ extern "C" {
  *
  * This format is highly platforms specific and not useful for cross-driver
  * sharing. It exists since on a given platform it does uniquely identify the
- * layout in a simple way for i915-specific userspace.
+ * layout in a simple way for i915-specific userspace. The format is
+ * ill-defined for platforms older than BDW.
  */
 #define I915_FORMAT_MOD_Y_TILED	fourcc_mod_code(INTEL, 2)
 
-- 
2.20.1