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Message-ID: <CAAFQd5DDpqZc41qKF_6mzOF3YAR_c6swisVDNSjapRFxHz2s9Q@mail.gmail.com>
Date: Thu, 9 Nov 2023 15:05:48 +0900
From: Tomasz Figa <tfiga@...omium.org>
To: Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc: mchehab@...nel.org, m.szyprowski@...sung.com, ming.qian@....com,
ezequiel@...guardiasur.com.ar, p.zabel@...gutronix.de,
gregkh@...uxfoundation.org, hverkuil-cisco@...all.nl,
nicolas.dufresne@...labora.com, linux-media@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
kernel@...labora.com
Subject: Re: [PATCH v14.1] media: videobuf2: Be more flexible on the number of
queue stored buffers
On Wed, Nov 8, 2023 at 10:56 PM Benjamin Gaignard
<benjamin.gaignard@...labora.com> wrote:
>
>
> Le 08/11/2023 à 11:24, Tomasz Figa a écrit :
> > On Mon, Nov 06, 2023 at 03:39:40PM +0100, Benjamin Gaignard wrote:
> >> Add 'max_num_buffers' field in vb2_queue struct to let drivers decide
> >> how many buffers could be stored in a queue.
> >> This require 'bufs' array to be allocated at queue init time and freed
> >> when releasing the queue.
> >> By default VB2_MAX_FRAME remains the limit.
> >>
> >> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> >> Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
> >> ---
> >> version 14.1:
> >> - Do not change the number of freed buffers in vb2_core_queue_release().
> >>
> >> .../media/common/videobuf2/videobuf2-core.c | 39 +++++++++++++++----
> >> .../media/common/videobuf2/videobuf2-v4l2.c | 6 +--
> >> include/media/videobuf2-core.h | 10 ++++-
> >> 3 files changed, 43 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> >> index c5c5ae4d213d..5711c6a130fd 100644
> >> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> >> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> >> @@ -416,7 +416,7 @@ static void init_buffer_cache_hints(struct vb2_queue *q, struct vb2_buffer *vb)
> >> */
> >> static void vb2_queue_add_buffer(struct vb2_queue *q, struct vb2_buffer *vb, unsigned int index)
> >> {
> >> - WARN_ON(index >= VB2_MAX_FRAME || q->bufs[index]);
> >> + WARN_ON(index >= q->max_num_buffers || q->bufs[index]);
> >>
> >> q->bufs[index] = vb;
> >> vb->index = index;
> >> @@ -449,9 +449,9 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
> >> struct vb2_buffer *vb;
> >> int ret;
> >>
> >> - /* Ensure that q->num_buffers+num_buffers is below VB2_MAX_FRAME */
> >> + /* Ensure that the number of already queue + num_buffers is below q->max_num_buffers */
> > Perhaps "the number of buffers already in the queue"?
>
> I will do that in the next version.
>
> >
> >> num_buffers = min_t(unsigned int, num_buffers,
> >> - VB2_MAX_FRAME - q_num_buffers);
> >> + q->max_num_buffers - q_num_buffers);
> >>
> >> for (buffer = 0; buffer < num_buffers; ++buffer) {
> >> /* Allocate vb2 buffer structures */
> >> @@ -813,7 +813,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
> >> unsigned plane_sizes[VB2_MAX_PLANES] = { };
> >> bool non_coherent_mem = flags & V4L2_MEMORY_FLAG_NON_COHERENT;
> >> unsigned int i;
> >> - int ret;
> >> + int ret = 0;
> >>
> >> if (q->streaming) {
> >> dprintk(q, 1, "streaming active\n");
> >> @@ -857,17 +857,22 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
> >> /*
> >> * Make sure the requested values and current defaults are sane.
> >> */
> >> - WARN_ON(q->min_buffers_needed > VB2_MAX_FRAME);
> > Do we really want to remove this warning completely?
>
> Yes because VB2_MAX_FRAME is no more relevant.
Hmm, but we still have q->max_num_buffers. Although given your reply
to my other comment below, we may be able to just ensure the value is
valid in vb2_core_queue_init().
>
> >
> >> num_buffers = max_t(unsigned int, *count, q->min_buffers_needed);
> >> - num_buffers = min_t(unsigned int, num_buffers, VB2_MAX_FRAME);
> >> + num_buffers = min_t(unsigned int, num_buffers, q->max_num_buffers);
> >> memset(q->alloc_devs, 0, sizeof(q->alloc_devs));
> >> /*
> >> * Set this now to ensure that drivers see the correct q->memory value
> >> * in the queue_setup op.
> >> */
> >> mutex_lock(&q->mmap_lock);
> >> + if (!q->bufs)
> >> + q->bufs = kcalloc(q->max_num_buffers, sizeof(*q->bufs), GFP_KERNEL);
> > Shouldn't this happen in core code rather than the v4l2-specific ioctl
> > helper? Since we just allocate the maximum possible size, then maybe
> > vb2_core_queue_init()?
>
> Hans had already suggest that in a previous version but it appear that
> vb2_core_queue_init() and vb2_core_queue_release() aren't balanced so
> we got cases where queue aren't initialized before reqbufs or create_bufs
> that why I had to put this allocation here.
How about __vb2_queue_alloc()?
>
> >
> >> + if (!q->bufs)
> >> + ret = -ENOMEM;
> >> q->memory = memory;
> >> mutex_unlock(&q->mmap_lock);
> >> + if (ret)
> >> + return ret;
> >> set_queue_coherency(q, non_coherent_mem);
> >>
> >> /*
> >> @@ -976,7 +981,7 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
> >> bool no_previous_buffers = !q_num_bufs;
> >> int ret = 0;
> >>
> >> - if (q_num_bufs == VB2_MAX_FRAME) {
> >> + if (q->num_buffers == q->max_num_buffers) {
> >> dprintk(q, 1, "maximum number of buffers already allocated\n");
> >> return -ENOBUFS;
> >> }
> >> @@ -993,7 +998,13 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
> >> */
> >> mutex_lock(&q->mmap_lock);
> >> q->memory = memory;
> >> + if (!q->bufs)
> >> + q->bufs = kcalloc(q->max_num_buffers, sizeof(*q->bufs), GFP_KERNEL);
> > Ditto.
> >
> >> + if (!q->bufs)
> >> + ret = -ENOMEM;
> >> mutex_unlock(&q->mmap_lock);
> >> + if (ret)
> >> + return ret;
> >> q->waiting_for_buffers = !q->is_output;
> >> set_queue_coherency(q, non_coherent_mem);
> >> } else {
> >> @@ -1005,7 +1016,7 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
> >> return -EINVAL;
> >> }
> >>
> >> - num_buffers = min(*count, VB2_MAX_FRAME - q_num_bufs);
> >> + num_buffers = min(*count, q->max_num_buffers - q_num_bufs);
> >>
> >> if (requested_planes && requested_sizes) {
> >> num_planes = requested_planes;
> >> @@ -2465,6 +2476,12 @@ int vb2_core_queue_init(struct vb2_queue *q)
> >> /*
> >> * Sanity check
> >> */
> >> + if (!q->max_num_buffers)
> >> + q->max_num_buffers = VB2_MAX_FRAME;
> > Can we add a comment here to explain that this is for backwards
> > compatibility with drivers which don't support more buffers?
> >
> > Actually, we should probably document in kerneldoc for vb2_queue that 0 is
> > an allowed and special value.
>
> I will do that.
>
> >
> >> +
> >> + /* The maximum is limited by offset cookie encoding pattern */
> >> + q->max_num_buffers = min_t(unsigned int, q->max_num_buffers, MAX_BUFFER_INDEX);
> >> +
> >> if (WARN_ON(!q) ||
> >> WARN_ON(!q->ops) ||
> >> WARN_ON(!q->mem_ops) ||
> >> @@ -2474,6 +2491,10 @@ int vb2_core_queue_init(struct vb2_queue *q)
> >> WARN_ON(!q->ops->buf_queue))
> >> return -EINVAL;
> >>
> >> + if (WARN_ON(q->max_num_buffers > MAX_BUFFER_INDEX) ||
> > Hmm, how is this possible?
>
> MAX_BUFFER_INDEX depends on PAGE_SHIFT and, on some architectures,
> it can goes up to 15. In this MAX_BUFFER_INDEX is only equal to 512,
> that why this check in needed.
>
> >
> >> + WARN_ON(q->min_buffers_needed > q->max_num_buffers))
> >> + return -EINVAL;
> > I have a loose recollection that it's allowed for a driver to change this
> > value depending on the configuration. You may want to double check if any
> > driver doesn't do so already if we want to disallow that. (and also
> > document that it's not allowed)
>
> I don't think any driver change is value given the configuration but Hans wants
> to clarify the usage of this field on another series.
>
Okay, thanks.
> >
> >> +
> >> if (WARN_ON(q->requires_requests && !q->supports_requests))
> >> return -EINVAL;
> >>
> >> @@ -2520,6 +2541,8 @@ void vb2_core_queue_release(struct vb2_queue *q)
> >> __vb2_queue_cancel(q);
> >> mutex_lock(&q->mmap_lock);
> >> __vb2_queue_free(q, vb2_get_num_buffers(q));
> >> + kfree(q->bufs);
> >> + q->bufs = NULL;
> >> q->num_buffers = 0;
> >> mutex_unlock(&q->mmap_lock);
> >> }
> >> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> >> index 7d798fb15c0b..f3cf4b235c1f 100644
> >> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> >> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> >> @@ -627,7 +627,7 @@ struct vb2_buffer *vb2_find_buffer(struct vb2_queue *q, u64 timestamp)
> >> * This loop doesn't scale if there is a really large number of buffers.
> >> * Maybe something more efficient will be needed in this case.
> >> */
> >> - for (i = 0; i < vb2_get_num_buffers(q); i++) {
> >> + for (i = 0; i < q->max_num_buffers; i++) {
> >> vb2 = vb2_get_buffer(q, i);
> >>
> >> if (!vb2)
> >> @@ -1142,7 +1142,7 @@ int _vb2_fop_release(struct file *file, struct mutex *lock)
> >>
> >> if (lock)
> >> mutex_lock(lock);
> >> - if (file->private_data == vdev->queue->owner) {
> >> + if (!vdev->queue->owner || file->private_data == vdev->queue->owner) {
> >> vb2_queue_release(vdev->queue);
> >> vdev->queue->owner = NULL;
> >> }
> >> @@ -1270,7 +1270,7 @@ void vb2_video_unregister_device(struct video_device *vdev)
> >> */
> >> get_device(&vdev->dev);
> >> video_unregister_device(vdev);
> >> - if (vdev->queue && vdev->queue->owner) {
> >> + if (vdev->queue) {
> >> struct mutex *lock = vdev->queue->lock ?
> >> vdev->queue->lock : vdev->lock;
> >>
> >> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> >> index 8f9d9e4af5b1..e77a397195f2 100644
> >> --- a/include/media/videobuf2-core.h
> >> +++ b/include/media/videobuf2-core.h
> >> @@ -558,6 +558,7 @@ struct vb2_buf_ops {
> >> * @dma_dir: DMA mapping direction.
> >> * @bufs: videobuf2 buffer structures
> >> * @num_buffers: number of allocated/used buffers
> >> + * @max_num_buffers: upper limit of number of allocated/used buffers
> >> * @queued_list: list of buffers currently queued from userspace
> >> * @queued_count: number of buffers queued and ready for streaming.
> >> * @owned_by_drv_count: number of buffers owned by the driver
> >> @@ -619,8 +620,9 @@ struct vb2_queue {
> >> struct mutex mmap_lock;
> >> unsigned int memory;
> >> enum dma_data_direction dma_dir;
> >> - struct vb2_buffer *bufs[VB2_MAX_FRAME];
> >> + struct vb2_buffer **bufs;
> >> unsigned int num_buffers;
> >> + unsigned int max_num_buffers;
> >>
> >> struct list_head queued_list;
> >> unsigned int queued_count;
> >> @@ -1248,6 +1250,12 @@ static inline void vb2_clear_last_buffer_dequeued(struct vb2_queue *q)
> >> static inline struct vb2_buffer *vb2_get_buffer(struct vb2_queue *q,
> >> unsigned int index)
> >> {
> >> + if (!q->bufs)
> >> + return NULL;
> >> +
> >> + if (index >= q->max_num_buffers)
> > Wouldn't this be already prevented by the condition below?
>
> yes but the series will remove q->num_buffers after this patch
> so for me it make sense to introduce this check now.
>
Yeah, I realized it later. Thanks.
Best regards,
Tomasz
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