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/

5 files changed, 133 insertions, 0 deletions

diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index ca461b6cf71f..8254521b4583 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -594,6 +594,9 @@ void drm_atomic_set_fence_for_plane(struct drm_plane_state *plane_state,
 int __must_check
 drm_atomic_set_crtc_for_connector(struct drm_connector_state *conn_state,
 				  struct drm_crtc *crtc);
+int drm_atomic_set_writeback_fb_for_connector(
+		struct drm_connector_state *conn_state,
+		struct drm_framebuffer *fb);
 int __must_check
 drm_atomic_add_affected_connectors(struct drm_atomic_state *state,
 				   struct drm_crtc *crtc);
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index c5797c24edd3..716c3a0e0e1d 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -437,6 +437,19 @@ struct drm_connector_state {
 	 * protection. This is most commonly used for HDCP.
 	 */
 	unsigned int content_protection;
+
+	/**
+	 * @writeback_job: Writeback job for writeback connectors
+	 *
+	 * Holds the framebuffer for a writeback connector. As the writeback
+	 * completion may be asynchronous to the normal commit cycle, the
+	 * writeback job lifetime is managed separately from the normal atomic
+	 * state by this object.
+	 *
+	 * See also: drm_writeback_queue_job() and
+	 * drm_writeback_signal_completion()
+	 */
+	struct drm_writeback_job *writeback_job;
 };
 
 /**
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index fb45839179dd..5f24329e6927 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -784,6 +784,21 @@ struct drm_mode_config {
 	 */
 	struct drm_property *panel_orientation_property;
 
+	/**
+	 * @writeback_fb_id_property: Property for writeback connectors, storing
+	 * the ID of the output framebuffer.
+	 * See also: drm_writeback_connector_init()
+	 */
+	struct drm_property *writeback_fb_id_property;
+
+	/**
+	 * @writeback_pixel_formats_property: Property for writeback connectors,
+	 * storing an array of the supported pixel formats for the writeback
+	 * engine (read-only).
+	 * See also: drm_writeback_connector_init()
+	 */
+	struct drm_property *writeback_pixel_formats_property;
+
 	/* dumb ioctl parameters */
 	uint32_t preferred_depth, prefer_shadow;
 
diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 35e2a3a79fc5..3b289773297c 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -974,6 +974,17 @@ struct drm_connector_helper_funcs {
 	 */
 	int (*atomic_check)(struct drm_connector *connector,
 			    struct drm_connector_state *state);
+
+	/**
+	 * @atomic_commit:
+	 *
+	 * This hook is to be used by drivers implementing writeback connectors
+	 * that need a point when to commit the writeback job to the hardware.
+	 *
+	 * This callback is used by the atomic modeset helpers.
+	 */
+	void (*atomic_commit)(struct drm_connector *connector,
+			      struct drm_writeback_job *writeback_job);
 };
 
 /**
diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
new file mode 100644
index 000000000000..17cd1feecd7e
--- /dev/null
+++ b/include/drm/drm_writeback.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * (C) COPYRIGHT 2016 ARM Limited. All rights reserved.
+ * Author: Brian Starkey <brian.starkey@arm.com>
+ *
+ * This program is free software and is provided to you under the terms of the
+ * GNU General Public License version 2 as published by the Free Software
+ * Foundation, and any use by you of this program is subject to the terms
+ * of such GNU licence.
+ */
+
+#ifndef __DRM_WRITEBACK_H__
+#define __DRM_WRITEBACK_H__
+#include <drm/drm_connector.h>
+#include <drm/drm_encoder.h>
+#include <linux/workqueue.h>
+
+struct drm_writeback_connector {
+	struct drm_connector base;
+
+	/**
+	 * @encoder: Internal encoder used by the connector to fulfill
+	 * the DRM framework requirements. The users of the
+	 * @drm_writeback_connector control the behaviour of the @encoder
+	 * by passing the @enc_funcs parameter to drm_writeback_connector_init()
+	 * function.
+	 */
+	struct drm_encoder encoder;
+
+	/**
+	 * @pixel_formats_blob_ptr:
+	 *
+	 * DRM blob property data for the pixel formats list on writeback
+	 * connectors
+	 * See also drm_writeback_connector_init()
+	 */
+	struct drm_property_blob *pixel_formats_blob_ptr;
+
+	/** @job_lock: Protects job_queue */
+	spinlock_t job_lock;
+
+	/**
+	 * @job_queue:
+	 *
+	 * Holds a list of a connector's writeback jobs; the last item is the
+	 * most recent. The first item may be either waiting for the hardware
+	 * to begin writing, or currently being written.
+	 *
+	 * See also: drm_writeback_queue_job() and
+	 * drm_writeback_signal_completion()
+	 */
+	struct list_head job_queue;
+};
+
+struct drm_writeback_job {
+	/**
+	 * @cleanup_work:
+	 *
+	 * Used to allow drm_writeback_signal_completion to defer dropping the
+	 * framebuffer reference to a workqueue
+	 */
+	struct work_struct cleanup_work;
+
+	/**
+	 * @list_entry:
+	 *
+	 * List item for the writeback connector's @job_queue
+	 */
+	struct list_head list_entry;
+
+	/**
+	 * @fb:
+	 *
+	 * Framebuffer to be written to by the writeback connector. Do not set
+	 * directly, use drm_atomic_set_writeback_fb_for_connector()
+	 */
+	struct drm_framebuffer *fb;
+};
+
+int drm_writeback_connector_init(struct drm_device *dev,
+				 struct drm_writeback_connector *wb_connector,
+				 const struct drm_connector_funcs *con_funcs,
+				 const struct drm_encoder_helper_funcs *enc_helper_funcs,
+				 const u32 *formats, int n_formats);
+
+void drm_writeback_queue_job(struct drm_writeback_connector *wb_connector,
+			     struct drm_writeback_job *job);
+
+void drm_writeback_cleanup_job(struct drm_writeback_job *job);
+void drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector);
+#endif