[PATCH] drm/modes: Support video parameters with only reflect option

[Stephan Gerhold <stephan@gerhold.net>]

At the moment, video mode parameters like video=540x960,reflect_x,
(without rotation set) are silently ignored.

One of the reasons for this is that the calculation that
combines the panel_orientation with cmdline->rotation_reflection
does not handle the case when cmdline->rotation_reflection does
not have any rotation set.
(i.e. cmdline->rotation_reflection & DRM_MODE_ROTATE_MASK == 0)

Example:
  *rotation = DRM_MODE_ROTATE_0 (no panel_orientation)
  cmdline->rotation_reflection = DRM_MODE_REFLECT_X (video=MODE,reflect_x)

The current code does:
  panel_rot = ilog2(*rotation & DRM_MODE_ROTATE_MASK);
  cmdline_rot = ilog2(cmdline->rotation_reflection & DRM_MODE_ROTATE_MASK);
  sum_rot = (panel_rot + cmdline_rot) % 4;

and therefore:
  panel_rot = ilog2(DRM_MODE_ROTATE_0) = ilog2(1) = 0
  cmdline_rot = ilog2(0) = -1
  sum_rot = (0 + -1) % 4 = -1 % 4 = 3
   ...
  *rotation = DRM_MODE_ROTATE_270 | DRM_MODE_REFLECT_X

So we incorrectly generate DRM_MODE_ROTATE_270 in this case.
To prevent cmdline_rot from becoming -1, we need to treat
the rotation as DRM_MODE_ROTATE_0.

On the other hand, there is no need to go through that calculation
at all if no rotation is set in rotation_reflection.
A simple XOR is enough to combine the reflections.

Finally, also allow DRM_MODE_ROTATE_0 in the if statement below.
DRM_MODE_ROTATE_0 means "no rotation" and should therefore not
require any special handling (e.g. specific tiling format).

This makes video parameters with only reflect option work correctly.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
---
 drivers/gpu/drm/drm_client_modeset.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_client_modeset.c b/drivers/gpu/drm/drm_client_modeset.c
index 895b73f23079..cfebce4f19a5 100644
--- a/drivers/gpu/drm/drm_client_modeset.c
+++ b/drivers/gpu/drm/drm_client_modeset.c
@@ -859,19 +859,23 @@ bool drm_client_rotation(struct drm_mode_set *modeset, unsigned int *rotation)
 	 */
 	cmdline = &connector->cmdline_mode;
 	if (cmdline->specified && cmdline->rotation_reflection) {
-		unsigned int cmdline_rest, panel_rest;
-		unsigned int cmdline_rot, panel_rot;
-		unsigned int sum_rot, sum_rest;
+		if (cmdline->rotation_reflection & DRM_MODE_ROTATE_MASK) {
+			unsigned int cmdline_rest, panel_rest;
+			unsigned int cmdline_rot, panel_rot;
+			unsigned int sum_rot, sum_rest;
 
-		panel_rot = ilog2(*rotation & DRM_MODE_ROTATE_MASK);
-		cmdline_rot = ilog2(cmdline->rotation_reflection & DRM_MODE_ROTATE_MASK);
-		sum_rot = (panel_rot + cmdline_rot) % 4;
+			panel_rot = ilog2(*rotation & DRM_MODE_ROTATE_MASK);
+			cmdline_rot = ilog2(cmdline->rotation_reflection & DRM_MODE_ROTATE_MASK);
+			sum_rot = (panel_rot + cmdline_rot) % 4;
 
-		panel_rest = *rotation & ~DRM_MODE_ROTATE_MASK;
-		cmdline_rest = cmdline->rotation_reflection & ~DRM_MODE_ROTATE_MASK;
-		sum_rest = panel_rest ^ cmdline_rest;
+			panel_rest = *rotation & ~DRM_MODE_ROTATE_MASK;
+			cmdline_rest = cmdline->rotation_reflection & ~DRM_MODE_ROTATE_MASK;
+			sum_rest = panel_rest ^ cmdline_rest;
 
-		*rotation = (1 << sum_rot) | sum_rest;
+			*rotation = (1 << sum_rot) | sum_rest;
+		} else {
+			*rotation ^= cmdline->rotation_reflection;
+		}
 	}
 
 	/*
@@ -879,7 +883,8 @@ bool drm_client_rotation(struct drm_mode_set *modeset, unsigned int *rotation)
 	 * depending on the hardware this may require the framebuffer
 	 * to be in a specific tiling format.
 	 */
-	if ((*rotation & DRM_MODE_ROTATE_MASK) != DRM_MODE_ROTATE_180 ||
+	if (((*rotation & DRM_MODE_ROTATE_MASK) != DRM_MODE_ROTATE_0 &&
+	     (*rotation & DRM_MODE_ROTATE_MASK) != DRM_MODE_ROTATE_180) ||
 	    !plane->rotation_property)
 		return false;
 
-- 
2.24.0

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