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SubjectRe: [RFC v5 07/11] [media] vb2: add in-fence support to QBUF
2017-11-17 Mauro Carvalho Chehab <mchehab@osg.samsung.com>:

> Em Wed, 15 Nov 2017 15:10:53 -0200
> Gustavo Padovan <gustavo@padovan.org> escreveu:
>
> > 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;
> > + }
> > +
> > + 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);
> > +
>
> The above code sounds weird: it is called even if the user is not
> using fences.
>
> You should probably be doing something like:
>
> if (fence || q->last_fence) {
> vb->in_fence = __set_in_fence(q, vb, fence);
> ...
> }
>

Sure.

> > /*
> > * 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) {
>
> I guess the case where fences is not used is not covered here.
>
> You probably should add a check at __get_num_ready_buffers(q)
> as well, making it just return q->queued_count if fences isn't
> used.

We can't know that beforehand, some buffer ahead may have a fence,
but there is already a check for !fence for each buffer. If none of
them have fences the return will be equal to q->queued_count.

Gustavo

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