[PATCH v14.1] media: videobuf2: Be more flexible on the number of queue stored buffers
Benjamin Gaignard
benjamin.gaignard at collabora.com
Wed Nov 8 05:56:31 PST 2023
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 at collabora.com>
>> Signed-off-by: Hans Verkuil <hverkuil-cisco at xs4all.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.
>
>> 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.
>
>> + 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.
>
>> +
>> 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.
Regards,
Benjamin
>
>> + return NULL;
>> +
>> if (index < q->num_buffers)
>> return q->bufs[index];
>> return NULL;
>> --
>> 2.39.2
>>
> Best regards,
> Tomasz
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