Re: [PATCH v7 4/6] [media] vb2: add in-fence support to QBUF

Hans Verkuil
2018-01-12T13:46:14Z

On 01/10/18 17:07, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.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 queue to the driver
> out of the order they were queued from userspace. That means that even if
> it fence signal it must wait 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.
>
> 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@collabora.com>
> ---
> drivers/media/common/videobuf/videobuf2-core.c | 166 ++++++++++++++++++++++---
> drivers/media/common/videobuf/videobuf2-v4l2.c | 29 ++++-
> drivers/media/v4l2-core/Kconfig | 33 +++++
> include/media/videobuf2-core.h | 14 ++-
> 4 files changed, 221 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/media/common/videobuf/videobuf2-core.c b/drivers/media/common/videobuf/videobuf2-core.c
> index f7109f827f6e..777e3a2bc746 100644
> --- a/drivers/media/common/videobuf/videobuf2-core.c
> +++ b/drivers/media/common/videobuf/videobuf2-core.c
> @@ -352,6 +352,7 @@ 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];
> @@ -936,7 +937,7 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
>
> switch (state) {
> case VB2_BUF_STATE_QUEUED:
> - return;
> + break;
> case VB2_BUF_STATE_REQUEUEING:
> if (q->start_streaming_called)
> __enqueue_in_driver(vb);
> @@ -946,6 +947,19 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
> wake_up(&q->done_wq);
> break;
> }
> +
> + /*
> + * The check below verifies if there is a buffer in queue with an

s/in/in the/

> + * error state. They are added to queue in the error state when
> + * their in-fence fails to signal.
> + * To not mess with buffer ordering we wait until the previous buffer
> + * is done to mark the buffer in the error state as done and notify
> + * userspace. So everytime a buffer is done we check the next one for

s/everytime/every time/

> + * VB2_BUF_STATE_ERROR.
> + */
> + vb = list_next_entry(vb, queued_entry);
> + if (vb && vb->state == VB2_BUF_STATE_ERROR)
> + vb2_buffer_done(vb, vb->state);

Hmm. I'm not sure this is correct. Please test this and make sure you have
enabled CONFIG_VIDEO_ADV_DEBUG. This enables additional instrumentation that
will warn if the internal vb2 state becomes unbalanced.

An additional problem I have with this recursive call is what happens when
a whole bunch of in fences signal an error, so you have e.g. 10 consecutive
buffers with state ERROR. You'd recurse 10 times in that case.

I think you are better off handling this corner case explicitly, e.g. something
like this:

for (;;) {
vb = list_next_entry(vb, queued_entry);
if (!vb || vb->state != VB2_BUF_STATE_ERROR)
break;

dprintk(4, "done processing on buffer %d, state: %d\n",
vb->index, vb->state);

if (state == VB2_BUF_STATE_QUEUED) {
vb->state = state;
} else {
spin_lock_irqsave(&q->done_lock, flags);
/* Add the buffer to the done buffers list */
list_add_tail(&vb->done_entry, &q->done_list);
spin_unlock_irqrestore(&q->done_lock, flags);

/* Inform any processes that may be waiting for buffers */
wake_up(&q->done_wq);
}

trace_vb2_buf_done(q, vb);
}

I *think* this ensures all counters remain balanced, but this really needs
to be tested. I haven't compiled this code, so I hope I got it right.

> }
> EXPORT_SYMBOL_GPL(vb2_buffer_done);
>
> @@ -1230,6 +1244,9 @@ 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);
>
> @@ -1281,6 +1298,24 @@ 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;
> + unsigned long flags;
> +
> + /* count num of buffers ready in front of the queued_list */
> + list_for_each_entry(vb, &q->queued_list, queued_entry) {
> + spin_lock_irqsave(&vb->fence_cb_lock, flags);
> + if (vb->in_fence && !dma_fence_is_signaled(vb->in_fence))
> + break;
> + ready_count++;
> + spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
> + }
> +
> + return ready_count;
> +}
> +
> int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb)
> {
> struct vb2_buffer *vb;
> @@ -1369,9 +1404,43 @@ 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 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 the fence signal with an error we mark the buffer as such

s/signal/signals/

> + * and avoid using it by setting it to VB2_BUF_STATE_ERROR and
> + * not queueing it to the driver. However we can't notify the error
> + * to userspace right now because, at the time this callback run, QBUF
> + * returned already.
> + * So we delay that to DQBUF time. See comments in vb2_buffer_done()
> + * as well.
> + */
> + if (vb->in_fence->error)
> + vb->state = VB2_BUF_STATE_ERROR;
> +
> + dma_fence_put(vb->in_fence);
> + vb->in_fence = NULL;
> +
> + if (vb->state == VB2_BUF_STATE_ERROR) {
> + spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
> + return;
> + }
> +
> + if (q->start_streaming_called)
> + __enqueue_in_driver(vb);
> + spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
> +}
> +
> +int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
> + struct dma_fence *fence)
> {
> struct vb2_buffer *vb;
> + unsigned long flags;
> int ret;
>
> vb = q->bufs[index];
> @@ -1380,16 +1449,18 @@ 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;
> }
>
> /*
> @@ -1400,6 +1471,7 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb)
> q->queued_count++;
> q->waiting_for_buffers = false;
> vb->state = VB2_BUF_STATE_QUEUED;
> + vb->in_fence = fence;
>
> if (pb)
> call_void_bufop(q, copy_timestamp, vb, pb);
> @@ -1407,15 +1479,42 @@ 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.
> + * 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 (q->start_streaming_called)
> - __enqueue_in_driver(vb);
> + spin_lock_irqsave(&vb->fence_cb_lock, flags);
> + if (vb->in_fence) {
> + ret = dma_fence_add_callback(vb->in_fence, &vb->fence_cb,
> + vb2_qbuf_fence_cb);
> + if (ret == -EINVAL) {
> + spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
> + goto err;
> + } else if (!ret) {
> + goto fill;
> + }
>
> - /* Fill buffer information for the userspace */
> - if (pb)
> - call_void_bufop(q, fill_user_buffer, vb, pb);
> + dma_fence_put(vb->in_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) {
> + struct vb2_buffer *b;

Add empty line.

> + list_for_each_entry(b, &q->queued_list, queued_entry) {
> + if (b->state != VB2_BUF_STATE_QUEUED)
> + continue;
> + if (b->in_fence)
> + break;
> + __enqueue_in_driver(b);
> + }
> + }
>
> /*
> * If streamon has been called, and we haven't yet called
> @@ -1424,14 +1523,33 @@ 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;

You're missing a spin_unlock_irqrestore() call in this error path.

> }
>
> + spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
> +
> + /* 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:
> + /* Fill buffer information for the userspace */
> + if (pb)
> + call_void_bufop(q, fill_user_buffer, vb, pb);
> +
> + if (vb->in_fence) {
> + dma_fence_put(vb->in_fence);
> + vb->in_fence = NULL;
> + }
> +
> + return ret;
> +
> }
> EXPORT_SYMBOL_GPL(vb2_core_qbuf);
>
> @@ -1642,6 +1760,8 @@ 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
> @@ -1672,6 +1792,16 @@ 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);
> + }
> +
> /*
> * Remove all buffers from videobuf's list...
> */
> @@ -1733,7 +1863,7 @@ 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;
> @@ -2255,7 +2385,7 @@ 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;
> @@ -2434,7 +2564,7 @@ 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;
> @@ -2537,7 +2667,7 @@ 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/videobuf/videobuf2-v4l2.c b/drivers/media/common/videobuf/videobuf2-v4l2.c
> index d838524a459e..0a41e3bb7733 100644
> --- a/drivers/media/common/videobuf/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf/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) &&

Wouldn't 'b->fence_fd > 0' be more sensible?

And possibly just set fence_fd to 0 if it is < 0.

> + !(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 = 0;
> b->reserved = 0;
>
> + 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
> @@ -562,6 +574,7 @@ 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)) {
> @@ -570,7 +583,19 @@ 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/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
> index bf52fbd07aed..a39968eb1d32 100644
> --- a/drivers/media/v4l2-core/Kconfig
> +++ b/drivers/media/v4l2-core/Kconfig
> @@ -79,3 +79,36 @@ config VIDEOBUF_DMA_CONTIG
> config VIDEOBUF_DVB
> tristate
> select VIDEOBUF_GEN
> +
> +# Used by drivers that need Videobuf2 modules
> +config VIDEOBUF2_CORE
> + select DMA_SHARED_BUFFER
> + select SYNC_FILE
> + tristate
> +
> +config VIDEOBUF2_MEMOPS
> + tristate
> + select FRAME_VECTOR
> +
> +config VIDEOBUF2_DMA_CONTIG
> + tristate
> + depends on HAS_DMA
> + select VIDEOBUF2_CORE
> + select VIDEOBUF2_MEMOPS
> + select DMA_SHARED_BUFFER
> +
> +config VIDEOBUF2_VMALLOC
> + tristate
> + select VIDEOBUF2_CORE
> + select VIDEOBUF2_MEMOPS
> + select DMA_SHARED_BUFFER
> +
> +config VIDEOBUF2_DMA_SG
> + tristate
> + depends on HAS_DMA
> + select VIDEOBUF2_CORE
> + select VIDEOBUF2_MEMOPS
> +
> +config VIDEOBUF2_DVB
> + tristate
> + select VIDEOBUF2_CORE
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 583cdc06de79..0a2b1ac12dd0 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -17,6 +17,7 @@
> #include <linux/poll.h>
> #include <linux/dma-buf.h>
> #include <linux/bitops.h>
> +#include <linux/dma-fence.h>
>
> #define VB2_MAX_FRAME (32)
> #define VB2_MAX_PLANES (8)
> @@ -255,12 +256,21 @@ 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 receive from vb2 client to wait on before

receive -> received

> + * 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 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;
> + spinlock_t fence_cb_lock;
> +
> #ifdef CONFIG_VIDEO_ADV_DEBUG
> /*
> * Counters for how often these buffer-related ops are
> @@ -750,6 +760,7 @@ 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
> + * @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``.
> @@ -764,7 +775,8 @@ 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 *fence);
>
> /**
> * vb2_core_dqbuf() - Dequeue a buffer to the userspace
>

Regards,

Hans