Message-ID: <20180119131205.GD9598@jade>
Date:   Fri, 19 Jan 2018 11:12:05 -0200
From:   Gustavo Padovan <gustavo@...ovan.org>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     linux-media@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Shuah Khan <shuahkh@....samsung.com>,
        Pawel Osciak <pawel@...iak.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Sakari Ailus <sakari.ailus@....fi>,
        Brian Starkey <brian.starkey@....com>,
        Thierry Escande <thierry.escande@...labora.com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [PATCH v7 5/6] [media] vb2: add out-fence support to QBUF

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

> On 01/10/18 17:07, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@...labora.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@...labora.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

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