[PATCH 3/5] drm: Add drm_rotation_chain()

[ville.syrjala@xxxxxxxxxxxxxxx]

From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>

drm_rotation_chain() can be used to combine the plane and crtc rotations
to calculate the total rotation for a specific plane.

Cc: Sagar Kamble <sagar.a.kamble@xxxxxxxxx>
Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_crtc.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_crtc.h     |  2 ++
 2 files changed, 44 insertions(+)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 7077676..71d366f 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -4065,6 +4065,48 @@ unsigned int drm_rotation_simplify(unsigned int rotation,
 EXPORT_SYMBOL(drm_rotation_simplify);
 
 /**
+ * drm_rotation_chain() - Chain plane and crtc rotations together
+ * @crtc_rotation: rotation for the entire crtc
+ * @plane_rotation: rotation for the plane in relation to the crtc
+ *
+ * Given @crtc_rotation and @plane_rotation, this function will
+ * comptute the total rotation for the plane in relation to 0
+ * degree rotated crtc. This can be used eg. to implement full crtc
+ * rotation using just plane rotation in hardware. Obviously that
+ * requires that all planes must support rotation since the crtc
+ * itself won't rotate the composed scene.
+ */
+unsigned int drm_rotation_chain(unsigned int crtc_rotation,
+				unsigned int plane_rotation)
+{
+	unsigned int rotation;
+
+	/* add up the rotation angles */
+	rotation = 1 << ((ffs(plane_rotation & 0xf) + ffs(crtc_rotation & 0xf) - 2) % 4);
+
+	/* plane reflection before plane rotation */
+	rotation |= plane_rotation & (BIT(DRM_REFLECT_X) | BIT(DRM_REFLECT_Y));
+
+	/* crtc reflection after plane rotation and before crtc rotation */
+	switch (plane_rotation & 0xf) {
+	case BIT(DRM_ROTATE_0):
+	case BIT(DRM_ROTATE_180):
+		rotation ^= crtc_rotation & (BIT(DRM_REFLECT_X) | BIT(DRM_REFLECT_Y));
+		break;
+	case BIT(DRM_ROTATE_90):
+	case BIT(DRM_ROTATE_270):
+		if (crtc_rotation & BIT(DRM_REFLECT_X))
+			rotation ^= BIT(DRM_REFLECT_Y);
+		if (crtc_rotation & BIT(DRM_REFLECT_Y))
+			rotation ^= BIT(DRM_REFLECT_X);
+		break;
+	}
+
+	return rotation;
+}
+EXPORT_SYMBOL(drm_rotation_chain);
+
+/**
  * drm_mode_config_init - initialize DRM mode_configuration structure
  * @dev: DRM device
  *
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index ee84a4a..ebb9bf4 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1189,6 +1189,8 @@ extern struct drm_property *drm_mode_create_rotation_property(struct drm_device
 							      unsigned int supported_rotations);
 extern unsigned int drm_rotation_simplify(unsigned int rotation,
 					  unsigned int supported_rotations);
+extern unsigned int drm_rotation_chain(unsigned int crtc_rotation,
+				       unsigned int plane_rotation);
 
 /* Helpers */
 static inline struct drm_crtc *drm_crtc_find(struct drm_device *dev,
-- 
1.8.3.2

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