linux-kernel - [PATCH 1/3] drm: drm_blend.c: Add precision in drm_rotation

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Message-Id: <20240409-google-drm-doc-v1-1-033d55cc8250@bootlin.com>
Date: Tue, 09 Apr 2024 12:04:05 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 seanpaul@...gle.com, marcheu@...gle.com, nicolejadeyee@...gle.com, 
 pekka.paalanen@...labora.com, thomas.petazzoni@...tlin.com, 
 Louis Chauvet <louis.chauvet@...tlin.com>
Subject: [PATCH 1/3] drm: drm_blend.c: Add precision in
 drm_rotation_simplify kernel doc

As the function uses non-trivial bit operations, add a little paragraph
to describe what is the expected behavior.

Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
---
 drivers/gpu/drm/drm_blend.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
index 6e74de833466..8d4b317eb9d7 100644
--- a/drivers/gpu/drm/drm_blend.c
+++ b/drivers/gpu/drm/drm_blend.c
@@ -321,6 +321,11 @@ EXPORT_SYMBOL(drm_plane_create_rotation_property);
  * transforms the hardware supports, this function may not
  * be able to produce a supported transform, so the caller should
  * check the result afterwards.
+ *
+ * If the rotation is not fully supported, this function will add a rotation of 180
+ * (ROTATE_90 would become ROTATE_270) and add a reflection on X and Y.
+ * The resulting transformation is the same (REFLECT_X | REFLECT_Y | ROTATE_180
+ * is a no-op), but some unsupported flags are removed.
  */
 unsigned int drm_rotation_simplify(unsigned int rotation,
 				   unsigned int supported_rotations)

-- 
2.43.0