[PATCH 1/1] drm/fourcc: Add documentation about software color conversion.

[Jocelyn Falempe <jfalempe@redhat.com>]

After discussions on IRC, the consensus is that the DRM drivers should
not do software color conversion, and only advertise the supported formats.
Update the doc accordingly so that the rule and exceptions are clear for
everyone.

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
---
 include/uapi/drm/drm_fourcc.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
index 8db7fd3f743e..00a29152da9f 100644
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/drm/drm_fourcc.h
@@ -38,6 +38,13 @@ extern "C" {
  * fourcc code, a Format Modifier may optionally be provided, in order to
  * further describe the buffer's format - for example tiling or compression.
  *
+ * DRM drivers should not do software color conversion, and only advertise the
+ * format they support in hardware. But there are two exceptions:
+ * The first is to support XRGB8888 if the hardware doesn't support it, because
+ * it's the de facto standard for userspace applications.
+ * The second is to drop the unused bits when sending the data to the hardware,
+ * to improve the bandwidth, like dropping the "X" in XRGB8888.
+ *
  * Format Modifiers
  * ----------------
  *
-- 
2.41.0