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.
v2: Rephrase comment (Daniel)
Signed-off-by: Mika Kahola <mika.kahola@xxxxxxxxx>
---
include/uapi/drm/drm_fourcc.h | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
index 8bc0b31597d8..9e488d10f8b4 100644
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/drm/drm_fourcc.h
@@ -354,9 +354,12 @@ extern "C" {
* a platform-dependent stride. On top of that the memory can apply
* platform-depending swizzling of some higher address bits into bit6.
*
- * 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.
+ * Note that this layout is only accurate on intel gen 8+ or valleyview chipsets.
+ * On earlier platforms the 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, which
+ * facilitated conversion of userspace to modifiers. Additionally the exact
+ * format on some really old platforms is not known.
*/
#define I915_FORMAT_MOD_X_TILED fourcc_mod_code(INTEL, 1)
@@ -369,9 +372,12 @@ extern "C" {
* memory can apply platform-depending swizzling of some higher address bits
* into bit6.
*
- * 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.
+ * Note that this layout is only accurate on intel gen 8+ or valleyview chipsets.
+ * On earlier platforms the 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, which
+ * facilitated conversion of userspace to modifiers. Additionally the exact
+ * format on some really old platforms is not known.
*/
#define I915_FORMAT_MOD_Y_TILED fourcc_mod_code(INTEL, 2)
--
2.20.1
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