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SubjectRe: [RFC v5 07/11] [media] vb2: add in-fence support to QBUF
Date
Hi Gustavo,

I am coming a bit late in this series' review, so apologies if some of my
comments have already have been discussed in an earlier revision.

On Thursday, November 16, 2017 2:10:53 AM JST, 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.
>
> To make that possible 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.
>
> 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/v4l2-core/Kconfig | 1 +
> drivers/media/v4l2-core/videobuf2-core.c | 202
> ++++++++++++++++++++++++++++---
> drivers/media/v4l2-core/videobuf2-v4l2.c | 29 ++++-
> include/media/videobuf2-core.h | 17 ++-
> 4 files changed, 231 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..26de4c80717d 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -23,6 +23,7 @@
> #include <linux/sched.h>
> #include <linux/freezer.h>
> #include <linux/kthread.h>
> +#include <linux/dma-fence-array.h>
>
> #include <media/videobuf2-core.h>
> #include <media/v4l2-mc.h>
> @@ -346,6 +347,7 @@ 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 +1224,9 @@ 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 +1278,23 @@ 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))
> + 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;
> @@ -1361,9 +1383,87 @@ 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;
> + }
> +
> + /*
> + * We always guarantee the ordering of buffers queued from
> + * userspace to be the same it is queued to the driver. For that
> + * 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 (fence && q->last_fence) {
> + struct dma_fence **fences;
> + struct dma_fence_array *arr;
> +
> + if (fence->context == q->last_fence->context) {
> + if (fence->seqno - q->last_fence->seqno <= INT_MAX) {
> + dma_fence_put(q->last_fence);
> + q->last_fence = dma_fence_get(fence);
> + } else {
> + dma_fence_put(fence);
> + fence = dma_fence_get(q->last_fence);
> + }
> + return fence;
> + }
> +
> + 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;
> +
> + q->last_fence = dma_fence_get(fence);
> + } else if (!fence && q->last_fence) {
> + fence = dma_fence_get(q->last_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;
> + }

Is this block necessary? IIUC the callback will never be set on buffers
without
an input fence, so (!vb->in_fence) should never be satisfied.

> +
> + dma_fence_put(vb->in_fence);
> + vb->in_fence = NULL;
> +
> + 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];
> @@ -1372,16 +1472,18 @@ 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 +1500,83 @@ 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)) {
> + dma_fence_put(fence);
> + ret = PTR_ERR(vb->in_fence);
> + goto err;
> + }
> + fence = NULL;
> +
> + /*
> + * 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 (vb->in_fence && !q->start_streaming_called &&
> + __get_num_ready_buffers(q) == q->min_buffers_needed - 1)
> + dma_fence_wait(vb->in_fence, true);

Mmm, that's a tough call. Userspace may unexpectingly block due to this
(which
fences are supposed to prevent), not sure how much of a problem this may
be.

> +
> /*
> * 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.
> + */
> + 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;
> + }
> +
> + dma_fence_put(vb->in_fence);
> + vb->in_fence = NULL;

I suppose the last two lines are supposed to be called when
dma_fence_add_callback() returns -ENOENT, because the fence has already
been
signaled? In that case I think the code would be more readable if you made
it
more explicit, something like:

// fence already signaled?
if (ret == -ENOENT) {
dma_fence_put(vb->in_fence);
vb->in_fence = NULL;
} else if (ret != 0) {
spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
goto err;
}

and that way you can get rid of the short-ranged fill: label.

> + }
> +
> +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);

Since that code was previously called when vb2_start_streaming() wasn't, we
had a guarantee that the buffer was only queued once. Now I wonder if we
could
not run into a situation where __enqueue_in_driver is called twice for the
last
queued buffer, once by vb2_start_streaming() and once here, now that
vb2_start_streaming() has set q->start_streaming_called to 1?

> + 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:
> + if (vb->in_fence) {
> + dma_fence_put(vb->in_fence);
> + vb->in_fence = NULL;
> + }
> +
> + return ret;
> +
> }
> EXPORT_SYMBOL_GPL(vb2_core_qbuf);
>
> @@ -1632,6 +1787,8 @@ 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 +1816,21 @@ 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 +1892,7 @@ 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 +2412,7 @@ 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 +2591,7 @@ 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 +2694,7 @@ 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) &&

Why do we need to consider both values invalid? Can 0 ever be a valid fence
fd?

For completeness you may also want to check the case where (b->fence_fd ==
-1 &&
(b->flags & V4L2_BUF_FLAG_IN_FENCE)) and return an error ahead of time, but
I
suppose the call to sync_file_get_fence() later on will catch this as well.

> + !(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 38b9c8dd42c6..5f48c7be7770 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
> @@ -504,6 +514,7 @@ struct vb2_buf_ops {
> * @last_buffer_dequeued: used in poll() and DQBUF to
> immediately return if the
> * last decoded buffer was already dequeued. Set for capture queues
> * when a buffer with the V4L2_BUF_FLAG_LAST is dequeued.
> + * @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
> */
> @@ -558,6 +569,8 @@ struct vb2_queue {
> unsigned int copy_timestamp:1;
> unsigned int last_buffer_dequeued:1;
>
> + struct dma_fence *last_fence;
> +
> struct vb2_fileio_data *fileio;
> struct vb2_threadio_data *threadio;
>
> @@ -733,6 +746,7 @@ 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.
> @@ -747,7 +761,8 @@ 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

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