[PATCH 03/36] drm/plane: Add optional ->atomic_disable() callback

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

In order to prevent drivers from having to perform the same checks over
and over again, add an optional ->atomic_disable callback which the core
calls under the right circumstances.

v2: pass old state and detect edges to avoid calling ->atomic_disable on
already disabled planes, remove redundant comment (Daniel Vetter)

v3: rename helper to drm_atomic_plane_disabling() to clarify that it is
checking for transitions, move helper to drm_atomic_helper.h, clarify
check for !old_state and its relation to transitional helpers

Signed-off-by: Thierry Reding <treding at nvidia.com>
---
 drivers/gpu/drm/drm_atomic_helper.c |  9 ++++++++-
 drivers/gpu/drm/drm_plane_helper.c  | 10 +++++++++-
 include/drm/drm_atomic_helper.h     | 37 +++++++++++++++++++++++++++++++++++++
 include/drm/drm_plane_helper.h      |  3 +++
 4 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 010661f23035..1cb04402cd73 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1113,7 +1113,14 @@ void drm_atomic_helper_commit_planes(struct drm_device *dev,
 
 		old_plane_state = old_state->plane_states[i];
 
-		funcs->atomic_update(plane, old_plane_state);
+		/*
+		 * Special-case disabling the plane if drivers support it.
+		 */
+		if (drm_atomic_plane_disabling(plane, old_plane_state) &&
+		    funcs->atomic_disable)
+			funcs->atomic_disable(plane, old_plane_state);
+		else
+			funcs->atomic_update(plane, old_plane_state);
 	}
 
 	for (i = 0; i < ncrtcs; i++) {
diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c
index 2f961c180273..02c1a0b74e04 100644
--- a/drivers/gpu/drm/drm_plane_helper.c
+++ b/drivers/gpu/drm/drm_plane_helper.c
@@ -449,7 +449,15 @@ int drm_plane_helper_commit(struct drm_plane *plane,
 			crtc_funcs[i]->atomic_begin(crtc[i]);
 	}
 
-	plane_funcs->atomic_update(plane, plane_state);
+	/*
+	 * Drivers may optionally implement the ->atomic_disable callback, so
+	 * special-case that here.
+	 */
+	if (drm_atomic_plane_disabling(plane, plane_state) &&
+	    plane_funcs->atomic_disable)
+		plane_funcs->atomic_disable(plane, plane_state);
+	else
+		plane_funcs->atomic_update(plane, plane_state);
 
 	for (i = 0; i < 2; i++) {
 		if (crtc_funcs[i] && crtc_funcs[i]->atomic_flush)
diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
index 2095917ff8c7..a0ea4ded3cb5 100644
--- a/include/drm/drm_atomic_helper.h
+++ b/include/drm/drm_atomic_helper.h
@@ -127,4 +127,41 @@ void drm_atomic_helper_connector_destroy_state(struct drm_connector *connector,
 #define drm_atomic_crtc_state_for_each_plane(plane, crtc_state) \
 	drm_for_each_plane_mask(plane, (crtc_state)->state->dev, (crtc_state)->plane_mask)
 
+/*
+ * drm_atomic_plane_disabling - check whether a plane is being disabled
+ * @plane: plane object
+ * @old_state: previous atomic state
+ *
+ * Checks the atomic state of a plane to determine whether it's being disabled
+ * or not. This also WARNs if it detects an invalid state (both CRTC and FB
+ * need to either both be NULL or both be non-NULL).
+ *
+ * RETURNS:
+ * True if the plane is being disabled, false otherwise.
+ */
+static inline bool
+drm_atomic_plane_disabling(struct drm_plane *plane,
+			   struct drm_plane_state *old_state)
+{
+	/*
+	 * When disabling a plane, CRTC and FB should always be NULL together.
+	 * Anything else should be considered a bug in the atomic core, so we
+	 * gently warn about it.
+	 */
+	WARN_ON((plane->state->crtc == NULL && plane->state->fb != NULL) ||
+		(plane->state->crtc != NULL && plane->state->fb == NULL));
+
+	/*
+	 * When using the transitional helpers, old_state may be NULL. If so,
+	 * we know nothing about the current state and have to assume that it
+	 * might be enabled.
+	 *
+	 * When using the atomic helpers, old_state won't be NULL. Therefore
+	 * this check assumes that either the driver will have reconstructed
+	 * the correct state in ->reset() or that the driver will have taken
+	 * appropriate measures to disable all planes.
+	 */
+	return (!old_state || old_state->crtc) && !plane->state->crtc;
+}
+
 #endif /* DRM_ATOMIC_HELPER_H_ */
diff --git a/include/drm/drm_plane_helper.h b/include/drm/drm_plane_helper.h
index 0f2230311aa8..680be61ef20a 100644
--- a/include/drm/drm_plane_helper.h
+++ b/include/drm/drm_plane_helper.h
@@ -52,6 +52,7 @@ int drm_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
  * @cleanup_fb: cleanup a framebuffer when it's no longer used by the plane
  * @atomic_check: check that a given atomic state is valid and can be applied
  * @atomic_update: apply an atomic state to the plane
+ * @atomic_disable: disable the plane
  *
  * The helper operations are called by the mid-layer CRTC helper.
  */
@@ -65,6 +66,8 @@ struct drm_plane_helper_funcs {
 			    struct drm_plane_state *state);
 	void (*atomic_update)(struct drm_plane *plane,
 			      struct drm_plane_state *old_state);
+	void (*atomic_disable)(struct drm_plane *plane,
+			       struct drm_plane_state *old_state);
 };
 
 static inline void drm_plane_helper_add(struct drm_plane *plane,
-- 
2.1.3