Message-Id: <20180521165946.11778-13-ezequiel@collabora.com>
Date:   Mon, 21 May 2018 13:59:42 -0300
From:   Ezequiel Garcia <ezequiel@...labora.com>
To:     linux-media@...r.kernel.org
Cc:     kernel@...labora.com, Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Shuah Khan <shuahkh@....samsung.com>,
        Pawel Osciak <pawel@...iak.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Sakari Ailus <sakari.ailus@....fi>,
        Brian Starkey <brian.starkey@....com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Ezequiel Garcia <ezequiel@...labora.com>
Subject: [PATCH v10 12/16] vb2: add in-fence support to QBUF

From: Gustavo Padovan <gustavo.padovan@...labora.com>

Receive in-fence from userspace and add support for waiting on them
before queueing the buffer to the driver. Buffers can't be queued to the
driver before its fences signal. And a buffer can't be queued to the driver
out of the order they were queued from userspace. That means that even if
its fence signals it must wait for all other buffers, ahead of it in the queue,
to signal first.

If the fence for some buffer fails we do not queue it to the driver,
instead we mark it as error and wait until the previous buffer is done
to notify userspace of the error. We wait here to deliver the buffers back
to userspace in order.

v13: - cleanup implementation.
     - remove wrong Kconfig changes.
     - print noisy warning on unexpected enqueue conditioin
     - schedule a vb2_start_streaming work from the fence callback

v12: fixed dvb_vb2.c usage of vb2_core_qbuf.

v11: - minor doc/comments fixes (Hans Verkuil)
     - reviewed the in-fence path at __fill_v4l2_buffer()

v10: - rename fence to in_fence in many places
     - handle fences signalling with error better (Hans Verkuil)

v9: - improve comments and docs (Hans Verkuil)
    - fix unlocking of vb->fence_cb_lock on vb2_core_qbuf (Hans Verkuil)
    - move in-fences code that was in the out-fences patch here (Alex)

v8: - improve comments about fences with errors

v7: - get rid of the fence array stuff for ordering and just use
      get_num_buffers_ready() (Hans)
    - fix issue of queuing the buffer twice (Hans)
    - avoid the dma_fence_wait() in core_qbuf() (Alex)
    - merge preparation commit in

v6: - With fences always keep the order userspace queues the buffers.
    - Protect in_fence manipulation with a lock (Brian Starkey)
    - check if fences have the same context before adding a fence array
    - Fix last_fence ref unbalance in __set_in_fence() (Brian Starkey)
    - Clean up fence if __set_in_fence() fails (Brian Starkey)
    - treat -EINVAL from dma_fence_add_callback() (Brian Starkey)

v5: - use fence_array to keep buffers ordered in vb2 core when
      needed (Brian Starkey)
    - keep backward compat on the reserved2 field (Brian Starkey)
    - protect fence callback removal with lock (Brian Starkey)

v4: - Add a comment about dma_fence_add_callback() not returning a
      error (Hans)
    - Call dma_fence_put(vb->in_fence) if fence signaled (Hans)
    - select SYNC_FILE under config VIDEOBUF2_CORE (Hans)
    - Move dma_fence_is_signaled() check to __enqueue_in_driver() (Hans)
    - Remove list_for_each_entry() in __vb2_core_qbuf() (Hans)
    - Remove if (vb->state != VB2_BUF_STATE_QUEUED) from
      vb2_start_streaming() (Hans)
    - set IN_FENCE flags on __fill_v4l2_buffer (Hans)
    - Queue buffers to the driver as soon as they are ready (Hans)
    - call fill_user_buffer() after queuing the buffer (Hans)
    - add err: label to clean up fence
    - add dma_fence_wait() before calling vb2_start_streaming()

v3: - document fence parameter
    - remove ternary if at vb2_qbuf() return (Mauro)
    - do not change if conditions behaviour (Mauro)

v2: - fix vb2_queue_or_prepare_buf() ret check
    - remove check for VB2_MEMORY_DMABUF only (Javier)
    - check num of ready buffers to start streaming
    - when queueing, start from the first ready buffer
    - handle queue cancel

Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
---
 drivers/media/common/videobuf2/Kconfig          |   1 +
 drivers/media/common/videobuf2/videobuf2-core.c | 224 ++++++++++++++++++++----
 drivers/media/common/videobuf2/videobuf2-v4l2.c |  37 +++-
 drivers/media/dvb-core/dvb_vb2.c                |   2 +-
 include/media/videobuf2-core.h                  |  19 +-
 5 files changed, 242 insertions(+), 41 deletions(-)

diff --git a/drivers/media/common/videobuf2/Kconfig b/drivers/media/common/videobuf2/Kconfig
index 17c32ea58395..27ad9e8a268b 100644
--- a/drivers/media/common/videobuf2/Kconfig
+++ b/drivers/media/common/videobuf2/Kconfig
@@ -1,6 +1,7 @@
 # Used by drivers that need Videobuf2 modules
 config VIDEOBUF2_CORE
 	select DMA_SHARED_BUFFER
+	select SYNC_FILE
 	tristate
 
 config VIDEOBUF2_V4L2
diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index a9a0a9d1decb..86b5ebe25263 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -27,6 +27,7 @@
 #include <linux/kthread.h>
 
 #include <media/videobuf2-core.h>
+#include <media/v4l2-ioctl.h>
 #include <media/v4l2-mc.h>
 
 #include <trace/events/vb2.h>
@@ -189,6 +190,7 @@ module_param(debug, int, 0644);
 
 static void __vb2_queue_cancel(struct vb2_queue *q);
 static void __enqueue_in_driver(struct vb2_buffer *vb);
+static void __qbuf_work(struct work_struct *work);
 
 static void __vb2_buffer_free(struct kref *kref)
 {
@@ -373,6 +375,7 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
 		vb->index = q->num_buffers + buffer;
 		vb->type = q->type;
 		vb->memory = memory;
+		INIT_WORK(&vb->qbuf_work, __qbuf_work);
 		for (plane = 0; plane < num_planes; ++plane) {
 			vb->planes[plane].length = plane_sizes[plane];
 			vb->planes[plane].min_length = plane_sizes[plane];
@@ -932,21 +935,12 @@ void *vb2_plane_cookie(struct vb2_buffer *vb, unsigned int plane_no)
 }
 EXPORT_SYMBOL_GPL(vb2_plane_cookie);
 
-void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
+static void vb2_process_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
 {
 	struct vb2_queue *q = vb->vb2_queue;
 	unsigned long flags;
 	unsigned int plane;
 
-	if (WARN_ON(vb->state != VB2_BUF_STATE_ACTIVE))
-		return;
-
-	if (WARN_ON(state != VB2_BUF_STATE_DONE &&
-		    state != VB2_BUF_STATE_ERROR &&
-		    state != VB2_BUF_STATE_QUEUED &&
-		    state != VB2_BUF_STATE_REQUEUEING))
-		state = VB2_BUF_STATE_ERROR;
-
 #ifdef CONFIG_VIDEO_ADV_DEBUG
 	/*
 	 * Although this is not a callback, it still does have to balance
@@ -962,6 +956,9 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
 		call_void_memop(vb, finish, vb->planes[plane].mem_priv);
 
 	spin_lock_irqsave(&q->done_lock, flags);
+	if (vb->state == VB2_BUF_STATE_ACTIVE)
+		atomic_dec(&q->owned_by_drv_count);
+
 	if (state == VB2_BUF_STATE_QUEUED ||
 	    state == VB2_BUF_STATE_REQUEUEING) {
 		vb->state = VB2_BUF_STATE_QUEUED;
@@ -970,7 +967,7 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
 		list_add_tail(&vb->done_entry, &q->done_list);
 		vb->state = state;
 	}
-	atomic_dec(&q->owned_by_drv_count);
+
 	spin_unlock_irqrestore(&q->done_lock, flags);
 
 	trace_vb2_buf_done(q, vb);
@@ -987,6 +984,47 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
 		wake_up(&q->done_wq);
 		break;
 	}
+
+}
+
+void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
+{
+	struct vb2_buffer *next;
+	struct vb2_queue *q;
+
+	dprintk(4, "called done on buffer %d state: %d -> %d\n",
+			vb->index, vb->state, state);
+
+	if (vb->state == VB2_BUF_STATE_ERROR)
+		return;
+	if (WARN_ON(vb->state != VB2_BUF_STATE_ACTIVE))
+		return;
+
+	if (WARN_ON(state != VB2_BUF_STATE_DONE &&
+		    state != VB2_BUF_STATE_ERROR &&
+		    state != VB2_BUF_STATE_QUEUED &&
+		    state != VB2_BUF_STATE_REQUEUEING))
+		state = VB2_BUF_STATE_ERROR;
+
+	vb2_process_buffer_done(vb, state);
+
+	/*
+	 * Check if there is any buffer with an in-fence error in the next
+	 * position of the queue. Buffers whose in-fence signaled with error
+	 * are not queued to the driver and kept on the queue until the buffer
+	 * before them is done.
+	 * So here we process any existing buffers with in-fence errors and
+	 * wake up userspace.
+	 */
+	q = vb->vb2_queue;
+	next = list_next_entry(vb, queued_entry);
+	list_for_each_entry_from(next, &q->queued_list, queued_entry) {
+		if (!next->in_fence || !next->in_fence->error)
+			break;
+		if (next->in_fence && next->in_fence->error &&
+		    vb->state != VB2_BUF_STATE_ERROR)
+			vb2_process_buffer_done(next, VB2_BUF_STATE_ERROR);
+	}
 }
 EXPORT_SYMBOL_GPL(vb2_buffer_done);
 
@@ -1271,6 +1309,8 @@ static void __enqueue_in_driver(struct vb2_buffer *vb)
 {
 	struct vb2_queue *q = vb->vb2_queue;
 
+	if (WARN_ON(vb->state == VB2_BUF_STATE_ACTIVE))
+		return;
 	vb->state = VB2_BUF_STATE_ACTIVE;
 	atomic_inc(&q->owned_by_drv_count);
 
@@ -1322,6 +1362,25 @@ static int __buf_prepare(struct vb2_buffer *vb, const void *pb)
 	return 0;
 }
 
+static int __get_num_ready_buffers(struct vb2_queue *q)
+{
+	struct vb2_buffer *vb;
+	int ready_count = 0;
+
+	/*
+	 * Count num of buffers ready in front of the queued_list.
+	 * We want to stop counting when we find a buffer with an
+	 * unsignaled fence.
+	 */
+	list_for_each_entry(vb, &q->queued_list, queued_entry) {
+		if (vb->in_fence && dma_fence_get_status(vb->in_fence) == 0)
+			break;
+		ready_count++;
+	}
+
+	return ready_count;
+}
+
 int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb)
 {
 	struct vb2_buffer *vb;
@@ -1338,7 +1397,7 @@ int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb)
 	if (ret)
 		return ret;
 
-	/* Fill buffer information for the userspace */
+	/* Fill buffer information for userspace */
 	call_void_bufop(q, fill_user_buffer, vb, pb);
 
 	dprintk(2, "prepare of buffer %d succeeded\n", vb->index);
@@ -1364,11 +1423,16 @@ static int vb2_start_streaming(struct vb2_queue *q)
 	int ret;
 
 	/*
-	 * If any buffers were queued before streamon,
-	 * we can now pass them to driver for processing.
+	 * Activate all buffers currently queued,
+	 * until we get an unsignaled fence.
 	 */
-	list_for_each_entry(vb, &q->queued_list, queued_entry)
+	list_for_each_entry(vb, &q->queued_list, queued_entry) {
+		if (vb->state != VB2_BUF_STATE_QUEUED)
+			continue;
+		if (vb->in_fence && dma_fence_get_status(vb->in_fence) == 0)
+			break;
 		__enqueue_in_driver(vb);
+	}
 
 	/* Tell the driver to start streaming */
 	q->start_streaming_called = 1;
@@ -1410,7 +1474,41 @@ static int vb2_start_streaming(struct vb2_queue *q)
 	return ret;
 }
 
-int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
+static void __qbuf_work(struct work_struct *work)
+{
+	struct vb2_buffer *vb;
+	struct vb2_queue *q;
+
+	vb = container_of(work, struct vb2_buffer, qbuf_work);
+	q = vb->vb2_queue;
+
+	if (q->lock)
+		mutex_lock(q->lock);
+	/* By the time we run, the buffer state could have changed,
+	 * so we need to check it's in the queued state.
+	 * This is the only valid state.
+	 */
+	if (q->start_streaming_called && vb->state == VB2_BUF_STATE_QUEUED)
+		__enqueue_in_driver(vb);
+
+	if (q->streaming && !q->start_streaming_called &&
+	    __get_num_ready_buffers(q) >= q->min_buffers_needed)
+		vb2_start_streaming(q);
+
+	if (q->lock)
+		mutex_unlock(q->lock);
+	__vb2_buffer_put(vb);
+}
+
+static void vb2_qbuf_fence_cb(struct dma_fence *f, struct dma_fence_cb *cb)
+{
+	struct vb2_buffer *vb = container_of(cb, struct vb2_buffer, fence_cb);
+
+	schedule_work(&vb->qbuf_work);
+}
+
+int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
+		  struct dma_fence *in_fence)
 {
 	struct vb2_buffer *vb;
 	int ret;
@@ -1421,16 +1519,18 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
 	case VB2_BUF_STATE_DEQUEUED:
 		ret = __buf_prepare(vb, pb);
 		if (ret)
-			return ret;
+			goto err_release;
 		break;
 	case VB2_BUF_STATE_PREPARED:
 		break;
 	case VB2_BUF_STATE_PREPARING:
 		dprintk(1, "buffer still being prepared\n");
-		return -EINVAL;
+		ret = -EINVAL;
+		goto err_release;
 	default:
 		dprintk(1, "invalid buffer state %d\n", vb->state);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto err_release;
 	}
 
 	/*
@@ -1448,15 +1548,44 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
 	trace_vb2_qbuf(q, vb);
 
 	/*
-	 * If already streaming, give the buffer to driver for processing.
-	 * If not, the buffer will be given to driver on next streamon.
+	 * If the fence didn't signal yet, we setup a callback to queue
+	 * the buffer once the fence signals. If the fence already signaled,
+	 * then we lose the reference and queue the buffer.
 	 */
-	if (q->start_streaming_called)
-		__enqueue_in_driver(vb);
+	if (in_fence) {
+		WARN_ON(vb->in_fence);
+		vb->in_fence = in_fence;
+		__vb2_buffer_get(vb);
+		ret = dma_fence_add_callback(in_fence, &vb->fence_cb,
+					     vb2_qbuf_fence_cb);
+		/* is the fence signaled? */
+		if (ret == -ENOENT) {
+			if (in_fence->error)
+				/* error-signaled fence, reject this buffer */
+				goto err_release;
+			dma_fence_put(in_fence);
+			vb->in_fence = NULL;
+			__vb2_buffer_put(vb);
+		} else if (ret) {
+			goto err_release;
+		}
+	}
 
-	/* Fill buffer information for the userspace */
-	if (pb)
-		call_void_bufop(q, fill_user_buffer, vb, pb);
+	/*
+	 * If already streaming and there is no fence to wait on
+	 * give the buffer to driver for processing.
+	 */
+	if (q->start_streaming_called) {
+		struct vb2_buffer *b;
+
+		list_for_each_entry(b, &q->queued_list, queued_entry) {
+			if (b->state != VB2_BUF_STATE_QUEUED)
+				continue;
+			if (b->in_fence && dma_fence_get_status(b->in_fence) == 0)
+				break;
+			__enqueue_in_driver(b);
+		}
+	}
 
 	/*
 	 * If streamon has been called, and we haven't yet called
@@ -1465,14 +1594,32 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
 	 * then we can finally call start_streaming().
 	 */
 	if (q->streaming && !q->start_streaming_called &&
-	    q->queued_count >= q->min_buffers_needed) {
+	    __get_num_ready_buffers(q) >= q->min_buffers_needed) {
 		ret = vb2_start_streaming(q);
 		if (ret)
-			return ret;
+			goto err_release;
 	}
 
+	/* Fill buffer information for userspace */
+	if (pb)
+		call_void_bufop(q, fill_user_buffer, vb, pb);
+
 	dprintk(2, "qbuf of buffer %d succeeded\n", vb->index);
 	return 0;
+
+err_release:
+	/* Fill buffer information for userspace */
+	if (pb)
+		call_void_bufop(q, fill_user_buffer, vb, pb);
+
+	if (in_fence) {
+		dma_fence_put(in_fence);
+		vb->in_fence = NULL;
+		__vb2_buffer_put(vb);
+	}
+
+	return ret;
+
 }
 EXPORT_SYMBOL_GPL(vb2_core_qbuf);
 
@@ -1615,7 +1762,12 @@ static void __vb2_dqbuf(struct vb2_buffer *vb)
 		return;
 
 	vb->state = VB2_BUF_STATE_DEQUEUED;
-
+	if (vb->in_fence) {
+		if (dma_fence_remove_callback(vb->in_fence, &vb->fence_cb))
+			__vb2_buffer_put(vb);
+		dma_fence_put(vb->in_fence);
+		vb->in_fence = NULL;
+	}
 	/* unmap DMABUF buffer */
 	if (q->memory == VB2_MEMORY_DMABUF)
 		for (i = 0; i < vb->num_planes; ++i) {
@@ -1653,7 +1805,7 @@ int vb2_core_dqbuf(struct vb2_queue *q, unsigned int *pindex, void *pb,
 	if (pindex)
 		*pindex = vb->index;
 
-	/* Fill buffer information for the userspace */
+	/* Fill buffer information for userspace */
 	if (pb)
 		call_void_bufop(q, fill_user_buffer, vb, pb);
 
@@ -1700,8 +1852,8 @@ static void __vb2_queue_cancel(struct vb2_queue *q)
 	if (WARN_ON(atomic_read(&q->owned_by_drv_count))) {
 		for (i = 0; i < q->num_buffers; ++i)
 			if (q->bufs[i]->state == VB2_BUF_STATE_ACTIVE) {
-				pr_warn("driver bug: stop_streaming operation is leaving buf %p in active state\n",
-					q->bufs[i]);
+				pr_warn("driver bug: stop_streaming operation is leaving buf[%d] 0x%p in active state\n",
+					q->bufs[i]->index, q->bufs[i]);
 				vb2_buffer_done(q->bufs[i], VB2_BUF_STATE_ERROR);
 			}
 		/* Must be zero now */
@@ -1783,7 +1935,7 @@ int vb2_core_streamon(struct vb2_queue *q, unsigned int type)
 	 * Tell driver to start streaming provided sufficient buffers
 	 * are available.
 	 */
-	if (q->queued_count >= q->min_buffers_needed) {
+	if (__get_num_ready_buffers(q) >= q->min_buffers_needed) {
 		ret = v4l_vb2q_enable_media_source(q);
 		if (ret)
 			return ret;
@@ -2305,7 +2457,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
 		 * Queue all buffers.
 		 */
 		for (i = 0; i < q->num_buffers; i++) {
-			ret = vb2_core_qbuf(q, i, NULL);
+			ret = vb2_core_qbuf(q, i, NULL, NULL);
 			if (ret)
 				goto err_reqbufs;
 			fileio->bufs[i].queued = 1;
@@ -2484,7 +2636,7 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
 
 		if (copy_timestamp)
 			b->timestamp = ktime_get_ns();
-		ret = vb2_core_qbuf(q, index, NULL);
+		ret = vb2_core_qbuf(q, index, NULL, NULL);
 		dprintk(5, "vb2_dbuf result: %d\n", ret);
 		if (ret)
 			return ret;
@@ -2587,7 +2739,7 @@ static int vb2_thread(void *data)
 		if (copy_timestamp)
 			vb->timestamp = ktime_get_ns();
 		if (!threadio->stop)
-			ret = vb2_core_qbuf(q, vb->index, NULL);
+			ret = vb2_core_qbuf(q, vb->index, NULL, NULL);
 		call_void_qop(q, wait_prepare, q);
 		if (ret || threadio->stop)
 			break;
diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index 8312f61adfa6..ac14cc8ab1c5 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -23,6 +23,7 @@
 #include <linux/sched.h>
 #include <linux/freezer.h>
 #include <linux/kthread.h>
+#include <linux/sync_file.h>
 
 #include <media/v4l2-dev.h>
 #include <media/v4l2-fh.h>
@@ -178,6 +179,22 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b,
 		return -EINVAL;
 	}
 
+	if ((b->fence_fd != 0 && b->fence_fd != -1) &&
+	    !(b->flags & V4L2_BUF_FLAG_IN_FENCE)) {
+		dprintk(1, "%s: fence_fd set without IN_FENCE flag\n", opname);
+		return -EINVAL;
+	}
+
+	if (b->fence_fd < 0 && (b->flags & V4L2_BUF_FLAG_IN_FENCE)) {
+		dprintk(1, "%s: IN_FENCE flag set but no fence_fd\n", opname);
+		return -EINVAL;
+	}
+
+	if ((b->flags & V4L2_BUF_FLAG_IN_FENCE) && !q->lock) {
+		pr_warn("%s: IN_FENCE flag set, but no queue lock\n", opname);
+		b->flags &= ~V4L2_BUF_FLAG_IN_FENCE;
+	}
+
 	return __verify_planes_array(q->bufs[b->index], b);
 }
 
@@ -210,6 +227,11 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, void *pb)
 	else
 		b->fence_fd = 0;
 
+	if (vb->in_fence)
+		b->flags |= V4L2_BUF_FLAG_IN_FENCE;
+	else
+		b->flags &= ~V4L2_BUF_FLAG_IN_FENCE;
+
 	if (q->is_multiplanar) {
 		/*
 		 * Fill in plane-related data if userspace provided an array
@@ -566,6 +588,7 @@ EXPORT_SYMBOL_GPL(vb2_create_bufs);
 
 int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
 {
+	struct dma_fence *in_fence = NULL;
 	int ret;
 
 	if (vb2_fileio_is_active(q)) {
@@ -574,7 +597,19 @@ int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
 	}
 
 	ret = vb2_queue_or_prepare_buf(q, b, "qbuf");
-	return ret ? ret : vb2_core_qbuf(q, b->index, b);
+	if (ret)
+		return ret;
+
+	if (b->flags & V4L2_BUF_FLAG_IN_FENCE) {
+		in_fence = sync_file_get_fence(b->fence_fd);
+		if (!in_fence) {
+			dprintk(1, "failed to get in-fence from fd %d\n",
+				b->fence_fd);
+			return -EINVAL;
+		}
+	}
+
+	return vb2_core_qbuf(q, b->index, b, in_fence);
 }
 EXPORT_SYMBOL_GPL(vb2_qbuf);
 
diff --git a/drivers/media/dvb-core/dvb_vb2.c b/drivers/media/dvb-core/dvb_vb2.c
index b811adf88afa..7da53f10db1a 100644
--- a/drivers/media/dvb-core/dvb_vb2.c
+++ b/drivers/media/dvb-core/dvb_vb2.c
@@ -385,7 +385,7 @@ int dvb_vb2_qbuf(struct dvb_vb2_ctx *ctx, struct dmx_buffer *b)
 {
 	int ret;
 
-	ret = vb2_core_qbuf(&ctx->vb_q, b->index, b);
+	ret = vb2_core_qbuf(&ctx->vb_q, b->index, b, NULL);
 	if (ret) {
 		dprintk(1, "[%s] index=%d errno=%d\n", ctx->name,
 			b->index, ret);
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 71538ae2c255..ddd555f59dbf 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -14,6 +14,7 @@
 
 #include <linux/bitops.h>
 #include <linux/dma-buf.h>
+#include <linux/dma-fence.h>
 #include <linux/kref.h>
 #include <linux/mm_types.h>
 #include <linux/mutex.h>
@@ -257,6 +258,10 @@ struct vb2_buffer {
 	 * done_entry:		entry on the list that stores all buffers ready
 	 *			to be dequeued to userspace
 	 * vb2_plane:		per-plane information; do not change
+	 * in_fence:		fence received from vb2 client to wait on before
+	 *			using the buffer (queueing to the driver)
+	 * fence_cb:		fence callback information
+	 * qbuf_work:		work for deferred qbuf operation
 	 */
 	struct kref		refcount;
 	enum vb2_buffer_state	state;
@@ -264,6 +269,11 @@ struct vb2_buffer {
 	struct vb2_plane	planes[VB2_MAX_PLANES];
 	struct list_head	queued_entry;
 	struct list_head	done_entry;
+
+	struct dma_fence	*in_fence;
+	struct dma_fence_cb	fence_cb;
+	struct work_struct	qbuf_work;
+
 #ifdef CONFIG_VIDEO_ADV_DEBUG
 	/*
 	 * Counters for how often these buffer-related ops are
@@ -488,8 +498,9 @@ struct vb2_buf_ops {
  * @lock:	pointer to a mutex that protects the &struct vb2_queue. The
  *		driver can set this to a mutex to let the v4l2 core serialize
  *		the queuing ioctls. If the driver wants to handle locking
- *		itself, then this should be set to NULL. This lock is not used
- *		by the videobuf2 core API.
+ *		itself, then this should be set to NULL. This lock is required
+ *		by the videobuf2 core only on the fence-deferred start streaming
+ *		path.
  * @owner:	The filehandle that 'owns' the buffers, i.e. the filehandle
  *		that called reqbufs, create_buffers or started fileio.
  *		This field is not used by the videobuf2 core API, but it allows
@@ -789,6 +800,7 @@ int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb);
  * @index:	id number of the buffer
  * @pb:		buffer structure passed from userspace to
  *		v4l2_ioctl_ops->vidioc_qbuf handler in driver
+ * @in_fence:	in-fence to wait on before queueing the buffer
  *
  * Videobuf2 core helper to implement VIDIOC_QBUF() operation. It is called
  * internally by VB2 by an API-specific handler, like ``videobuf2-v4l2.h``.
@@ -803,7 +815,8 @@ int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb);
  *
  * Return: returns zero on success; an error code otherwise.
  */
-int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb);
+int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
+		  struct dma_fence *in_fence);
 
 /**
  * vb2_core_dqbuf() - Dequeue a buffer to the userspace
-- 
2.16.3

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