[RFC v4 13/17] [media] vb2: add in-fence support to QBUF

From: Gustavo Padovan
Date: Fri Oct 20 2017 - 17:52:28 EST

From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>

Receive in-fence from userspace and add support for waiting on them
before queueing the buffer to the driver. Buffers are only queued
to the driver once they are ready. A buffer is ready when its
in-fence signals.

For queues that require vb2 to queue buffers to the v4l2 driver in same
order they are received from userspace we use fence_array to keep that
ordering. Basically we create a fence_array that contains both the current
fence and the fence from the previous buffer (which might be a fence array
as well). The base fence class for the fence_array becomes the new buffer
fence, waiting on that one guarantees that it won't be queued out of
order.

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

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@xxxxxxxxxxxxx>
---
drivers/media/v4l2-core/Kconfig | 1 +
drivers/media/v4l2-core/videobuf2-core.c | 179 ++++++++++++++++++++++++++++---
drivers/media/v4l2-core/videobuf2-v4l2.c | 29 ++++-
include/media/videobuf2-core.h | 17 ++-
4 files changed, 208 insertions(+), 18 deletions(-)

diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
index a35c33686abf..3f988c407c80 100644
--- a/drivers/media/v4l2-core/Kconfig
+++ b/drivers/media/v4l2-core/Kconfig
@@ -83,6 +83,7 @@ config VIDEOBUF_DVB
# Used by drivers that need Videobuf2 modules
config VIDEOBUF2_CORE
select DMA_SHARED_BUFFER
+ select SYNC_FILE
tristate

config VIDEOBUF2_MEMOPS
diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 60f8b582396a..78f369dba3e3 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -346,6 +346,7 @@ 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;
+ spin_lock_init(&vb->fence_cb_lock);
for (plane = 0; plane < num_planes; ++plane) {
vb->planes[plane].length = plane_sizes[plane];
vb->planes[plane].min_length = plane_sizes[plane];
@@ -1222,6 +1223,9 @@ static void __enqueue_in_driver(struct vb2_buffer *vb)
{
struct vb2_queue *q = vb->vb2_queue;

+ if (vb->in_fence && !dma_fence_is_signaled(vb->in_fence))
+ return;
+
vb->state = VB2_BUF_STATE_ACTIVE;
atomic_inc(&q->owned_by_drv_count);

@@ -1273,6 +1277,20 @@ 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 */
+ list_for_each_entry(vb, &q->queued_list, queued_entry) {
+ if (!vb->in_fence || dma_fence_is_signaled(vb->in_fence))
+ ready_count++;
+ }
+
+ return ready_count;
+}
+
int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb)
{
struct vb2_buffer *vb;
@@ -1361,7 +1379,74 @@ 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 struct dma_fence *__set_in_fence(struct vb2_queue *q,
+ struct vb2_buffer *vb,
+ struct dma_fence *fence)
+{
+ if (q->last_fence && dma_fence_is_signaled(q->last_fence)) {
+ dma_fence_put(q->last_fence);
+ q->last_fence = NULL;
+ }
+
+ /* For drivers that require the ordering of buffers queued from
+ * userspace to be the same it is queued to the driver - output
+ * some m2m devices - we create a fence array with the fence from
+ * the last queued buffer and this one, that way the fence for this
+ * buffer can't signal before the last one.
+ */
+ if (q->is_output || q->ordered_in_vb2) {
+ if (fence && q->last_fence) {
+ struct dma_fence **fences;
+ struct dma_fence_array *arr;
+
+ fences = kcalloc(2, sizeof(*fences), GFP_KERNEL);
+ if (!fences)
+ return ERR_PTR(-ENOMEM);
+
+ fences[0] = fence;
+ fences[1] = q->last_fence;
+
+ arr = dma_fence_array_create(2, fences,
+ dma_fence_context_alloc(1),
+ 1, false);
+ if (!arr) {
+ kfree(fences);
+ return ERR_PTR(-ENOMEM);
+ }
+
+ fence = &arr->base;
+ } else if (!fence && q->last_fence) {
+ fence = dma_fence_get(q->last_fence);
+ }
+
+ q->last_fence = dma_fence_get(fence);
+ }
+
+ return fence;
+}
+
+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);
+ struct vb2_queue *q = vb->vb2_queue;
+ unsigned long flags;
+
+ spin_lock_irqsave(&vb->fence_cb_lock, flags);
+ if (!vb->in_fence) {
+ spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
+ return;
+ }
+
+ dma_fence_put(vb->in_fence);
+ vb->in_fence = NULL;
+ spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
+
+ if (q->start_streaming_called)
+ __enqueue_in_driver(vb);
+}
+
+int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
+ struct dma_fence *fence)
{
struct vb2_buffer *vb;
int ret;
@@ -1372,16 +1457,18 @@ 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;
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;
default:
dprintk(1, "invalid buffer state %d\n", vb->state);
- return -EINVAL;
+ ret = -EINVAL;
+ goto err;
}

/*
@@ -1398,30 +1485,75 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)

trace_vb2_qbuf(q, vb);

+ vb->in_fence = __set_in_fence(q, vb, fence);
+ if (IS_ERR(vb->in_fence)) {
+ ret = PTR_ERR(vb->in_fence);
+ goto err;
+ }
+
+ /*
+ * If it is time to call vb2_start_streaming() wait for the fence
+ * to signal first. Of course, this happens only once per streaming.
+ * We want to run any step that might fail before we set the callback
+ * to queue the fence when it signals.
+ */
+ if (fence && !q->start_streaming_called &&
+ __get_num_ready_buffers(q) == q->min_buffers_needed - 1)
+ dma_fence_wait(fence, true);
+
/*
* If streamon has been called, and we haven't yet called
* start_streaming() since not enough buffers were queued, and
* we now have reached the minimum number of queued buffers,
* then we can finally call start_streaming().
- *
- * If already streaming, give the buffer to driver for processing.
- * If not, the buffer will be given to driver on next streamon.
*/
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;
- } else if (q->start_streaming_called) {
- __enqueue_in_driver(vb);
+ goto err;
+ }
+
+ /*
+ * For explicit synchronization: If the fence didn't signal
+ * yet we setup a callback to queue the buffer once the fence
+ * signals, and then, return successfully. But if the fence
+ * already signaled we lose the reference we held and queue the
+ * buffer to the driver.
+ */
+ if (fence) {
+ ret = dma_fence_add_callback(fence, &vb->fence_cb,
+ vb2_qbuf_fence_cb);
+ if (!ret)
+ goto fill;
+
+ dma_fence_put(fence);
+ vb->in_fence = NULL;
}

+fill:
+ /*
+ * If already streaming and there is no fence to wait on
+ * give the buffer to driver for processing.
+ */
+ if (q->start_streaming_called && !vb->in_fence)
+ __enqueue_in_driver(vb);
+
/* Fill buffer information for the 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:
+ if (vb->in_fence) {
+ dma_fence_put(vb->in_fence);
+ vb->in_fence = NULL;
+ }
+
+ return ret;
+
}
EXPORT_SYMBOL_GPL(vb2_core_qbuf);

@@ -1632,6 +1764,8 @@ EXPORT_SYMBOL_GPL(vb2_core_dqbuf);
static void __vb2_queue_cancel(struct vb2_queue *q)
{
unsigned int i;
+ struct vb2_buffer *vb;
+ unsigned long flags;

/*
* Tell driver to stop all transactions and release all queued
@@ -1659,6 +1793,21 @@ static void __vb2_queue_cancel(struct vb2_queue *q)
q->queued_count = 0;
q->error = 0;

+ list_for_each_entry(vb, &q->queued_list, queued_entry) {
+ spin_lock_irqsave(&vb->fence_cb_lock, flags);
+ if (vb->in_fence) {
+ dma_fence_remove_callback(vb->in_fence, &vb->fence_cb);
+ dma_fence_put(vb->in_fence);
+ vb->in_fence = NULL;
+ }
+ spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
+ }
+
+ if (q->last_fence) {
+ dma_fence_put(q->last_fence);
+ q->last_fence = NULL;
+ }
+
/*
* Remove all buffers from videobuf's list...
*/
@@ -1720,7 +1869,7 @@ 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;
@@ -2240,7 +2389,7 @@ 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;
@@ -2419,7 +2568,7 @@ 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;
@@ -2522,7 +2671,7 @@ 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/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c
index 110fb45fef6f..4c09ea007d90 100644
--- a/drivers/media/v4l2-core/videobuf2-v4l2.c
+++ b/drivers/media/v4l2-core/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 +179,12 @@ 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;
+ }
+
return __verify_planes_array(q->bufs[b->index], b);
}

@@ -203,9 +210,14 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, void *pb)
b->timestamp = ns_to_timeval(vb->timestamp);
b->timecode = vbuf->timecode;
b->sequence = vbuf->sequence;
- b->fence_fd = -1;
b->reserved = 0;

+ b->fence_fd = -1;
+ 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
@@ -560,6 +572,7 @@ EXPORT_SYMBOL_GPL(vb2_create_bufs);

int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b)
{
+ struct dma_fence *fence = NULL;
int ret;

if (vb2_fileio_is_active(q)) {
@@ -568,7 +581,19 @@ 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) {
+ fence = sync_file_get_fence(b->fence_fd);
+ if (!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, fence);
}
EXPORT_SYMBOL_GPL(vb2_qbuf);

diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index fc333e10e7d8..624ca2dce9ea 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -16,6 +16,7 @@
#include <linux/mutex.h>
#include <linux/poll.h>
#include <linux/dma-buf.h>
+#include <linux/dma-fence.h>

#define VB2_MAX_FRAME (32)
#define VB2_MAX_PLANES (8)
@@ -254,11 +255,20 @@ struct vb2_buffer {
* all buffers queued from userspace
* done_entry: entry on the list that stores all buffers ready
* to be dequeued to userspace
+ * in_fence: fence receive from vb2 client to wait on before
+ * using the buffer (queueing to the driver)
+ * fence_cb: fence callback information
+ * fence_cb_lock: protect callback signal/remove
*/
enum vb2_buffer_state state;

struct list_head queued_entry;
struct list_head done_entry;
+
+ struct dma_fence *in_fence;
+ struct dma_fence_cb fence_cb;
+ spinlock_t fence_cb_lock;
+
#ifdef CONFIG_VIDEO_ADV_DEBUG
/*
* Counters for how often these buffer-related ops are
@@ -508,6 +518,7 @@ struct vb2_buf_ops {
* @ordered_in_vb2: set by the driver to tell vb2 te guarantee the order
* of buffer queue from userspace with QBUF() until they are
* queued to the driver.
+ * @last_fence: last in-fence received. Used to keep ordering.
* @fileio: file io emulator internal data, used only if emulator is active
* @threadio: thread io internal data, used only if thread is active
*/
@@ -563,6 +574,8 @@ struct vb2_queue {
unsigned int ordered_in_driver:1;
unsigned int ordered_in_vb2:1;

+ struct dma_fence *last_fence;
+
struct vb2_fileio_data *fileio;
struct vb2_threadio_data *threadio;

@@ -738,6 +751,7 @@ 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 vidioc_qbuf handler
* in driver
+ * @fence: in-fence to wait on before queueing the buffer
*
* Should be called from vidioc_qbuf ioctl handler of a driver.
* The passed buffer should have been verified.
@@ -752,7 +766,8 @@ int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb);
* The return values from this function are intended to be directly returned
* from vidioc_qbuf handler in driver.
*/
-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 *fence);

/**
* vb2_core_dqbuf() - Dequeue a buffer to the userspace
--
2.13.6