Re: [PATCH v7 5/6] [media] vb2: add out-fence support to QBUF

Gustavo Padovan
2018-01-19T13:12:26Z

2018-01-12 Hans Verkuil <hverkuil@xs4all.nl>:

> On 01/10/18 17:07, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@collabora.com>
> >
> > If V4L2_BUF_FLAG_OUT_FENCE flag is present on the QBUF call we create
> > an out_fence and send its fd to userspace on the fence_fd field as a
> > return arg for the QBUF call.
> >
> > The fence is signaled on buffer_done(), when the job on the buffer is
> > finished.
> >
> > v8:
> > - return 0 as fence_fd if OUT_FENCE flag not used (Mauro)
> > - fix crash when checking not using fences in vb2_buffer_done()
> >
> > v7:
> > - merge patch that add the infrastructure to out-fences into
> > this one (Alex Courbot)
> > - Do not install the fd if there is no fence. (Alex Courbot)
> > - do not report error on requeueing, just WARN_ON_ONCE() (Hans)
> >
> > v6
> > - get rid of the V4L2_EVENT_OUT_FENCE event. We always keep the
> > ordering in vb2 for queueing in the driver, so the event is not
> > necessary anymore and the out_fence_fd is sent back to userspace
> > on QBUF call return arg
> > - do not allow requeueing with out-fences, instead mark the buffer
> > with an error and wake up to userspace.
> > - send the out_fence_fd back to userspace on the fence_fd field
> >
> > v5:
> > - delay fd_install to DQ_EVENT (Hans)
> > - if queue is fully ordered send OUT_FENCE event right away
> > (Brian)
> > - rename 'q->ordered' to 'q->ordered_in_driver'
> > - merge change to implement OUT_FENCE event here
> >
> > v4:
> > - return the out_fence_fd in the BUF_QUEUED event(Hans)
> >
> > v3: - add WARN_ON_ONCE(q->ordered) on requeueing (Hans)
> > - set the OUT_FENCE flag if there is a fence pending (Hans)
> > - call fd_install() after vb2_core_qbuf() (Hans)
> > - clean up fence if vb2_core_qbuf() fails (Hans)
> > - add list to store sync_file and fence for the next queued buffer
> >
> > v2: check if the queue is ordered.
> >
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
> > ---
> > drivers/media/common/videobuf/videobuf2-core.c | 101 +++++++++++++++++++++++--
> > drivers/media/common/videobuf/videobuf2-v4l2.c | 28 ++++++-
> > include/media/videobuf2-core.h | 22 ++++++
> > 3 files changed, 140 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/media/common/videobuf/videobuf2-core.c b/drivers/media/common/videobuf/videobuf2-core.c
> > index 777e3a2bc746..1f30d9efb7c8 100644
> > --- a/drivers/media/common/videobuf/videobuf2-core.c
> > +++ b/drivers/media/common/videobuf/videobuf2-core.c
> > @@ -25,6 +25,7 @@
> > #include <linux/sched.h>
> > #include <linux/freezer.h>
> > #include <linux/kthread.h>
> > +#include <linux/sync_file.h>
> >
> > #include <media/videobuf2-core.h>
> > #include <media/v4l2-mc.h>
> > @@ -357,6 +358,7 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
> > vb->planes[plane].length = plane_sizes[plane];
> > vb->planes[plane].min_length = plane_sizes[plane];
> > }
> > + vb->out_fence_fd = -1;
> > q->bufs[vb->index] = vb;
> >
> > /* Allocate video buffer memory for the MMAP type */
> > @@ -939,10 +941,22 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
> > case VB2_BUF_STATE_QUEUED:
> > break;
> > case VB2_BUF_STATE_REQUEUEING:
> > + /* Requeuing with explicit synchronization, spit warning */
> > + WARN_ON_ONCE(vb->out_fence);
> > +
> > if (q->start_streaming_called)
> > __enqueue_in_driver(vb);
> > - return;
> > + break;
> > default:
> > + if (vb->out_fence) {
> > + if (state == VB2_BUF_STATE_ERROR)
> > + dma_fence_set_error(vb->out_fence, -EFAULT);
> > + dma_fence_signal(vb->out_fence);
> > + dma_fence_put(vb->out_fence);
> > + vb->out_fence = NULL;
> > + vb->out_fence_fd = -1;
> > + }
> > +
> > /* Inform any processes that may be waiting for buffers */
> > wake_up(&q->done_wq);
> > break;
> > @@ -1341,6 +1355,65 @@ int vb2_core_prepare_buf(struct vb2_queue *q, unsigned int index, void *pb)
> > }
> > EXPORT_SYMBOL_GPL(vb2_core_prepare_buf);
> >
> > +static inline const char *vb2_fence_get_driver_name(struct dma_fence *fence)
> > +{
> > + return "vb2_fence";
> > +}
> > +
> > +static inline const char *vb2_fence_get_timeline_name(struct dma_fence *fence)
> > +{
> > + return "vb2_fence_timeline";
> > +}
> > +
> > +static inline bool vb2_fence_enable_signaling(struct dma_fence *fence)
> > +{
> > + return true;
> > +}
> > +
> > +static const struct dma_fence_ops vb2_fence_ops = {
> > + .get_driver_name = vb2_fence_get_driver_name,
> > + .get_timeline_name = vb2_fence_get_timeline_name,
> > + .enable_signaling = vb2_fence_enable_signaling,
> > + .wait = dma_fence_default_wait,
> > +};
> > +
> > +int vb2_setup_out_fence(struct vb2_queue *q, unsigned int index)
> > +{
> > + struct vb2_buffer *vb;
> > + u64 context;
> > +
> > + vb = q->bufs[index];
> > +
> > + vb->out_fence_fd = get_unused_fd_flags(O_CLOEXEC);
> > +
> > + if (call_qop(q, is_unordered, q))
> > + context = dma_fence_context_alloc(1);
> > + else
> > + context = q->out_fence_context;
> > +
> > + vb->out_fence = kzalloc(sizeof(*vb->out_fence), GFP_KERNEL);
> > + if (!vb->out_fence)
> > + return -ENOMEM;
> > +
> > + dma_fence_init(vb->out_fence, &vb2_fence_ops, &q->out_fence_lock,
> > + context, 1);
> > + if (!vb->out_fence) {
> > + put_unused_fd(vb->out_fence_fd);
> > + return -ENOMEM;
> > + }
> > +
> > + vb->sync_file = sync_file_create(vb->out_fence);
> > + if (!vb->sync_file) {
> > + put_unused_fd(vb->out_fence_fd);
> > + dma_fence_put(vb->out_fence);
> > + vb->out_fence = NULL;
> > + return -ENOMEM;
> > + }
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(vb2_setup_out_fence);
> > +
> > /*
> > * vb2_start_streaming() - Attempt to start streaming.
> > * @q: videobuf2 queue
> > @@ -1489,18 +1562,16 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
>
> This function is now very confusing. The last argument is a fence, but it is set
> for both in and out fences, and the previous patch sets vb->in_fence to fence.
> Even though the fence passed in this case is an out fence.

It doesn't use it for both types of fence. vb2_core_qbuf() receives that
in-fence as parameter and assign it to vb->in_fence. That is all. Maybe
I should call the parameter in_fence to avoid confusion.

>
> I think it would be much easier to understand if you add both an in_fence and
> out_fence argument to this function.
>
> Is it possible to have both and in and out fence for the same buffer? I think
> it is and in that case you really need two fences.

Yes it is. I added infomation about this in the docs for the next series
of these patches.

>
> > if (vb->in_fence) {
> > ret = dma_fence_add_callback(vb->in_fence, &vb->fence_cb,
> > vb2_qbuf_fence_cb);
> > - if (ret == -EINVAL) {
> > + /* is the fence signaled? */
> > + if (ret == -ENOENT) {
> > + dma_fence_put(vb->in_fence);
> > + vb->in_fence = NULL;
> > + } else if (ret) {
> > 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;
> > }
> >
> > -fill:
> > /*
> > * If already streaming and there is no fence to wait on
> > * give the buffer to driver for processing.
> > @@ -1535,6 +1606,11 @@ int vb2_core_qbuf(struct vb2_queue *q, unsigned int index, void *pb,
> > if (pb)
> > call_void_bufop(q, fill_user_buffer, vb, pb);
> >
> > + if (vb->out_fence) {
> > + fd_install(vb->out_fence_fd, vb->sync_file->file);
> > + vb->sync_file = NULL;
> > + }
> > +
> > dprintk(2, "qbuf of buffer %d succeeded\n", vb->index);
> > return 0;
> >
> > @@ -1802,6 +1878,12 @@ static void __vb2_queue_cancel(struct vb2_queue *q)
> > spin_unlock_irqrestore(&vb->fence_cb_lock, flags);
> > }
> >
> > + /*
> > + * Renew out-fence context.
> > + */
> > + if (!call_qop(q, is_unordered, q))
> > + q->out_fence_context = dma_fence_context_alloc(1);
>
> I don't think this is the right place. If a driver implements is_unordered, then
> the return value depends on the format. And that isn't locked in until buffers
> are allocated (i.e. reqbufs or create_bufs is called). So that's the moment that
> you can set this up.

Yes. That is a leftover from when I was thinking ordering by driver.
I'll fix it.

>
> BTW: I noticed is_unordered() returned an int instead of a bool. I think a bool
> makes more sense.
>
> > +
> > /*
> > * Remove all buffers from videobuf's list...
> > */
> > @@ -2134,6 +2216,9 @@ int vb2_core_queue_init(struct vb2_queue *q)
> > spin_lock_init(&q->done_lock);
> > mutex_init(&q->mmap_lock);
> > init_waitqueue_head(&q->done_wq);
> > + if (!call_qop(q, is_unordered, q))
> > + q->out_fence_context = dma_fence_context_alloc(1);
>
> Same here: at this moment you do not know if the queue is ordered or
> unordered.
>
> > + spin_lock_init(&q->out_fence_lock);
> >
> > q->memory = VB2_MEMORY_UNKNOWN;
> >
> > diff --git a/drivers/media/common/videobuf/videobuf2-v4l2.c b/drivers/media/common/videobuf/videobuf2-v4l2.c
> > index 0a41e3bb7733..f1291c25323f 100644
> > --- a/drivers/media/common/videobuf/videobuf2-v4l2.c
> > +++ b/drivers/media/common/videobuf/videobuf2-v4l2.c
> > @@ -179,12 +179,16 @@ 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)) {
> > + if (b->fence_fd > 0 && !(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 == -1 && (b->flags & V4L2_BUF_FLAG_IN_FENCE)) {
>
> Shouldn't this be b->fence_fd <= 0?

0 is a valid fd, so b-fence_fd < 0
>
> > + dprintk(1, "%s: IN_FENCE flag set but no fence_fd\n", opname);
> > + return -EINVAL;
> > + }
> > +
> > return __verify_planes_array(q->bufs[b->index], b);
> > }
> >
> > @@ -212,7 +216,12 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, void *pb)
> > b->sequence = vbuf->sequence;
> > b->reserved = 0;
> >
> > - b->fence_fd = 0;
> > + if (b->flags & V4L2_BUF_FLAG_OUT_FENCE) {
> > + b->fence_fd = vb->out_fence_fd;
> > + } else {
> > + b->fence_fd = 0;
> > + }
> > +
> > if (vb->in_fence)
> > b->flags |= V4L2_BUF_FLAG_IN_FENCE;
> > else
> > @@ -491,6 +500,10 @@ int vb2_querybuf(struct vb2_queue *q, struct v4l2_buffer *b)
> > ret = __verify_planes_array(vb, b);
> > if (!ret)
> > vb2_core_querybuf(q, b->index, b);
> > +
> > + /* Do not return the out-fence fd on querybuf */
> > + if (vb->out_fence)
> > + b->fence_fd = -1;
>
> This does not hurt. We also return dmabuf fds in the same way in querybuf.
>
> I would drop this.
>
> > }
> > }
> >
> > + if (b->flags & V4L2_BUF_FLAG_OUT_FENCE) {
> > + ret = vb2_setup_out_fence(q, b->index);
> > + if (ret) {
> > + dprintk(1, "failed to set up out-fence\n");
> > + dma_fence_put(fence);
> > + return ret;
> > + }
> > + }
> > +
> > return vb2_core_qbuf(q, b->index, b, fence);
>
> Hmm. So if vb2_core_qbuf returns an error, we still have created the out fence?
> As mentioned above, it is very confusing that the same vb2_core_qbuf 'fence'
> argument is used for both in and out fences.

I'm confused on how you got this understanding that we are using the
fence argument for both. I wonder if I failing to see a mistake on my
side here.

It seems that one of your concerns here is how do we clean up the
out-fence if vb2_core_qbuf() fails. I thought I had this covered, I'll
add a task here to check on that.

Gustavo