drm: Add writeback connector type

Writeback connectors represent writeback engines which can write the
CRTC output to a memory framebuffer. Add a writeback connector type and
related support functions.

Drivers should initialize a writeback connector with
drm_writeback_connector_init() which takes care of setting up all the
writeback-specific details on top of the normal functionality of
drm_connector_init().

Writeback connectors have a WRITEBACK_FB_ID property, used to set the
output framebuffer, and a WRITEBACK_PIXEL_FORMATS blob used to expose the
supported writeback formats to userspace.

When a framebuffer is attached to a writeback connector with the
WRITEBACK_FB_ID property, it is used only once (for the commit in which
it was included), and userspace can never read back the value of
WRITEBACK_FB_ID. WRITEBACK_FB_ID can only be set if the connector is
attached to a CRTC.

Changes since v1:
 - Added drm_writeback.c + documentation
 - Added helper to initialize writeback connector in one go
 - Added core checks
 - Squashed into a single commit
 - Dropped the client cap
 - Writeback framebuffers are no longer persistent

Changes since v2:
 Daniel Vetter:
 - Subclass drm_connector to drm_writeback_connector
 - Relax check to allow CRTC to be set without an FB
 - Add some writeback_ prefixes
 - Drop PIXEL_FORMATS_SIZE property, as it was unnecessary
 Gustavo Padovan:
 - Add drm_writeback_job to handle writeback signalling centrally

Changes since v3:
 - Rebased
 - Rename PIXEL_FORMATS -> WRITEBACK_PIXEL_FORMATS

Chances since v4:
 - Embed a drm_encoder inside the drm_writeback_connector to
   reduce the amount of boilerplate code required from the drivers
   that are using it.

Changes since v5:
 - Added Rob Clark's atomic_commit() vfunc to connector helper
   funcs, so that writeback jobs are committed from atomic helpers
 - Updated create_writeback_properties() signature to return an
   error code rather than a boolean false for failure.
 - Free writeback job with the connector state rather than when
   doing the cleanup_work()

Changes since v7:
 - fix extraneous use of out_fence that is only introduced in a
   subsequent patch.

Changes since v8:
 - whitespace changes pull from subsequent patch

Changes since v9:
 - Revert the v6 changes that free the writeback job in the connector
   state cleanup and return to doing it in the cleanup_work() function

Signed-off-by: Brian Starkey <brian.starkey@arm.com>
[rebased and fixed conflicts]
Signed-off-by: Mihail Atanassov <mihail.atanassov@arm.com>
[rebased and added atomic_commit() vfunc for writeback jobs]
Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/229037/

drivers/gpu/drm/drm_atomic.c

@@ -30,6 +30,7 @@
 #include <drm/drm_atomic.h>
 #include <drm/drm_mode.h>
 #include <drm/drm_print.h>
+#include <drm/drm_writeback.h>
 #include <linux/sync_file.h>
 
 #include "drm_crtc_internal.h"
@@ -690,6 +691,45 @@ static void drm_atomic_crtc_print_state(struct drm_printer *p,
 		crtc->funcs->atomic_print_state(p, state);
 }
 
+/**
+ * drm_atomic_connector_check - check connector state
+ * @connector: connector to check
+ * @state: connector state to check
+ *
+ * Provides core sanity checks for connector state.
+ *
+ * RETURNS:
+ * Zero on success, error code on failure
+ */
+static int drm_atomic_connector_check(struct drm_connector *connector,
+		struct drm_connector_state *state)
+{
+	struct drm_crtc_state *crtc_state;
+	struct drm_writeback_job *writeback_job = state->writeback_job;
+
+	if ((connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK) || !writeback_job)
+		return 0;
+
+	if (writeback_job->fb && !state->crtc) {
+		DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] framebuffer without CRTC\n",
+				 connector->base.id, connector->name);
+		return -EINVAL;
+	}
+
+	if (state->crtc)
+		crtc_state = drm_atomic_get_existing_crtc_state(state->state,
+								state->crtc);
+
+	if (writeback_job->fb && !crtc_state->active) {
+		DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] has framebuffer, but [CRTC:%d] is off\n",
+				 connector->base.id, connector->name,
+				 state->crtc->base.id);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 /**
  * drm_atomic_get_plane_state - get plane state
  * @state: global atomic state object
@@ -1321,6 +1361,12 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
 			return -EINVAL;
 		}
 		state->content_protection = val;
+	} else if (property == config->writeback_fb_id_property) {
+		struct drm_framebuffer *fb = drm_framebuffer_lookup(dev, NULL, val);
+		int ret = drm_atomic_set_writeback_fb_for_connector(state, fb);
+		if (fb)
+			drm_framebuffer_put(fb);
+		return ret;
 	} else if (connector->funcs->atomic_set_property) {
 		return connector->funcs->atomic_set_property(connector,
 				state, property, val);
@@ -1407,6 +1453,9 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
 		*val = state->scaling_mode;
 	} else if (property == connector->content_protection_property) {
 		*val = state->content_protection;
+	} else if (property == config->writeback_fb_id_property) {
+		/* Writeback framebuffer is one-shot, write and forget */
+		*val = 0;
 	} else if (connector->funcs->atomic_get_property) {
 		return connector->funcs->atomic_get_property(connector,
 				state, property, val);
@@ -1631,6 +1680,70 @@ drm_atomic_set_crtc_for_connector(struct drm_connector_state *conn_state,
 }
 EXPORT_SYMBOL(drm_atomic_set_crtc_for_connector);
 
+/*
+ * drm_atomic_get_writeback_job - return or allocate a writeback job
+ * @conn_state: Connector state to get the job for
+ *
+ * Writeback jobs have a different lifetime to the atomic state they are
+ * associated with. This convenience function takes care of allocating a job
+ * if there isn't yet one associated with the connector state, otherwise
+ * it just returns the existing job.
+ *
+ * Returns: The writeback job for the given connector state
+ */
+static struct drm_writeback_job *
+drm_atomic_get_writeback_job(struct drm_connector_state *conn_state)
+{
+	WARN_ON(conn_state->connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK);
+
+	if (!conn_state->writeback_job)
+		conn_state->writeback_job =
+			kzalloc(sizeof(*conn_state->writeback_job), GFP_KERNEL);
+
+	return conn_state->writeback_job;
+}
+
+/**
+ * drm_atomic_set_writeback_fb_for_connector - set writeback framebuffer
+ * @conn_state: atomic state object for the connector
+ * @fb: fb to use for the connector
+ *
+ * This is used to set the framebuffer for a writeback connector, which outputs
+ * to a buffer instead of an actual physical connector.
+ * Changing the assigned framebuffer requires us to grab a reference to the new
+ * fb and drop the reference to the old fb, if there is one. This function
+ * takes care of all these details besides updating the pointer in the
+ * state object itself.
+ *
+ * Note: The only way conn_state can already have an fb set is if the commit
+ * sets the property more than once.
+ *
+ * See also: drm_writeback_connector_init()
+ *
+ * Returns: 0 on success
+ */
+int drm_atomic_set_writeback_fb_for_connector(
+		struct drm_connector_state *conn_state,
+		struct drm_framebuffer *fb)
+{
+	struct drm_writeback_job *job =
+		drm_atomic_get_writeback_job(conn_state);
+	if (!job)
+		return -ENOMEM;
+
+	drm_framebuffer_assign(&job->fb, fb);
+
+	if (fb)
+		DRM_DEBUG_ATOMIC("Set [FB:%d] for connector state %p\n",
+				 fb->base.id, conn_state);
+	else
+		DRM_DEBUG_ATOMIC("Set [NOFB] for connector state %p\n",
+				 conn_state);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_atomic_set_writeback_fb_for_connector);
+
 /**
  * drm_atomic_add_affected_connectors - add connectors for crtc
  * @state: atomic state
@@ -1752,6 +1865,8 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
 	struct drm_plane_state *plane_state;
 	struct drm_crtc *crtc;
 	struct drm_crtc_state *crtc_state;
+	struct drm_connector *conn;
+	struct drm_connector_state *conn_state;
 	int i, ret = 0;
 
 	DRM_DEBUG_ATOMIC("checking %p\n", state);
@@ -1774,6 +1889,15 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
 		}
 	}
 
+	for_each_new_connector_in_state(state, conn, conn_state, i) {
+		ret = drm_atomic_connector_check(conn, conn_state);
+		if (ret) {
+			DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] atomic core check failed\n",
+					 conn->base.id, conn->name);
+			return ret;
+		}
+	}
+
 	if (config->funcs->atomic_check)
 		ret = config->funcs->atomic_check(state->dev, state);