drm/vkms: Document pixel_argb_u16

The meaning of each member of the structure was not specified. To clarify
the format used and the reason behind those choices, add some
documentation.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Link: https://lore.kernel.org/r/20250415-yuv-v18-1-f2918f71ec4b@bootlin.com
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
index a74a7fc3a056..3b7b46dd026f 100644
--- a/drivers/gpu/drm/vkms/vkms_drv.h
+++ b/drivers/gpu/drm/vkms/vkms_drv.h
@@ -45,6 +45,23 @@ struct vkms_frame_info {
 	unsigned int rotation;
 };
 
+/**
+ * struct pixel_argb_u16 - Internal representation of a pixel color.
+ * @a: Alpha component value, stored in 16 bits, without padding, using
+ *     machine endianness
+ * @r: Red component value, stored in 16 bits, without padding, using
+ *     machine endianness
+ * @g: Green component value, stored in 16 bits, without padding, using
+ *     machine endianness
+ * @b: Blue component value, stored in 16 bits, without padding, using
+ *     machine endianness
+ *
+ * The goal of this structure is to keep enough precision to ensure
+ * correct composition results in VKMS and simplifying color
+ * manipulation by splitting each component into its own field.
+ * Caution: the byte ordering of this structure is machine-dependent,
+ * you can't cast it directly to AR48 or xR48.
+ */
 struct pixel_argb_u16 {
 	u16 a, r, g, b;
 };