| Message ID | 20240314153226.197445-3-benjamin.gaignard@collabora.com |
|---|---|
| State | Accepted |
| Commit | 6662edcd32ccf939849cd1cd4ff04733a20ef97a |
| Headers | show |
| Series | Add REMOVE_BUF ioctl | expand |
Em Thu, 14 Mar 2024 16:32:19 +0100 Benjamin Gaignard <benjamin.gaignard@collabora.com> escreveu: > Add 'min_reqbufs_allocation' field in the vb2_queue structure so drivers > can specify the minimum number of buffers to allocate when calling > VIDIOC_REQBUFS. > When initializing the queue, v4l2 core makes sure that the following > constraints are respected: > - the minimum number of buffers to allocate must be at least 2 because > one buffer is used by the hardware while the other is being processed > by userspace. > -if the driver needs 'min_queued_buffers' in the queue before calling > start_streaming(), then the minimum requirement is 'min_queued_buffers + 1' > to keep at least one buffer available for userspace. > > Simplify __vb2_init_fileio() by using 'min_reqbufs_allocation' directly > to avoid duplicating the minimum number of buffers to allocate computation. > > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com> LGTM. Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org> > --- > .../media/common/videobuf2/videobuf2-core.c | 38 +++++++++++-------- > include/media/videobuf2-core.h | 15 +++++++- > 2 files changed, 37 insertions(+), 16 deletions(-) > > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c > index d8b3c04cb3b5..58c495b253ce 100644 > --- a/drivers/media/common/videobuf2/videobuf2-core.c > +++ b/drivers/media/common/videobuf2/videobuf2-core.c > @@ -866,7 +866,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory, > /* > * Make sure the requested values and current defaults are sane. > */ > - num_buffers = max_t(unsigned int, *count, q->min_queued_buffers); > + num_buffers = max_t(unsigned int, *count, q->min_reqbufs_allocation); > num_buffers = min_t(unsigned int, num_buffers, q->max_num_buffers); > memset(q->alloc_devs, 0, sizeof(q->alloc_devs)); > /* > @@ -918,7 +918,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory, > * There is no point in continuing if we can't allocate the minimum > * number of buffers needed by this vb2_queue. > */ > - if (allocated_buffers < q->min_queued_buffers) > + if (allocated_buffers < q->min_reqbufs_allocation) > ret = -ENOMEM; > > /* > @@ -2524,6 +2524,25 @@ int vb2_core_queue_init(struct vb2_queue *q) > if (WARN_ON(q->supports_requests && q->min_queued_buffers)) > return -EINVAL; > > + /* > + * The minimum requirement is 2: one buffer is used > + * by the hardware while the other is being processed by userspace. > + */ > + if (q->min_reqbufs_allocation < 2) > + q->min_reqbufs_allocation = 2; > + > + /* > + * If the driver needs 'min_queued_buffers' in the queue before > + * calling start_streaming() then the minimum requirement is > + * 'min_queued_buffers + 1' to keep at least one buffer available > + * for userspace. > + */ > + if (q->min_reqbufs_allocation < q->min_queued_buffers + 1) > + q->min_reqbufs_allocation = q->min_queued_buffers + 1; > + > + if (WARN_ON(q->min_reqbufs_allocation > q->max_num_buffers)) > + return -EINVAL; > + > INIT_LIST_HEAD(&q->queued_list); > INIT_LIST_HEAD(&q->done_list); > spin_lock_init(&q->done_lock); > @@ -2717,7 +2736,6 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > struct vb2_fileio_data *fileio; > struct vb2_buffer *vb; > int i, ret; > - unsigned int count = 0; > > /* > * Sanity check > @@ -2738,18 +2756,8 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > if (q->streaming || vb2_get_num_buffers(q) > 0) > return -EBUSY; > > - /* > - * Start with q->min_queued_buffers + 1, driver can increase it in > - * queue_setup() > - * > - * 'min_queued_buffers' buffers need to be queued up before you > - * can start streaming, plus 1 for userspace (or in this case, > - * kernelspace) processing. > - */ > - count = max(2, q->min_queued_buffers + 1); > - > dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n", > - (read) ? "read" : "write", count, q->fileio_read_once, > + (read) ? "read" : "write", q->min_reqbufs_allocation, q->fileio_read_once, > q->fileio_write_immediately); > > fileio = kzalloc(sizeof(*fileio), GFP_KERNEL); > @@ -2763,7 +2771,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > * Request buffers and use MMAP type to force driver > * to allocate buffers by itself. > */ > - fileio->count = count; > + fileio->count = q->min_reqbufs_allocation; > fileio->memory = VB2_MEMORY_MMAP; > fileio->type = q->type; > q->fileio = fileio; > diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h > index 667bf9ee1101..4a8b9135cec8 100644 > --- a/include/media/videobuf2-core.h > +++ b/include/media/videobuf2-core.h > @@ -549,9 +549,21 @@ struct vb2_buf_ops { > * @start_streaming can be called. Used when a DMA engine > * cannot be started unless at least this number of buffers > * have been queued into the driver. > - * VIDIOC_REQBUFS will ensure at least @min_queued_buffers > + * VIDIOC_REQBUFS will ensure at least @min_queued_buffers + 1 > * buffers will be allocated. Note that VIDIOC_CREATE_BUFS will not > * modify the requested buffer count. > + * @min_reqbufs_allocation: the minimum number of buffers to be allocated when > + * calling VIDIOC_REQBUFS. Note that VIDIOC_CREATE_BUFS will *not* > + * modify the requested buffer count and does not use this field. > + * Drivers can set this if there has to be a certain number of > + * buffers available for the hardware to work effectively. > + * This allows calling VIDIOC_REQBUFS with a buffer count of 1 and > + * it will be automatically adjusted to a workable buffer count. > + * If set, then @min_reqbufs_allocation must be larger than > + * @min_queued_buffers + 1. > + * If this field is > 3, then it is highly recommended that the > + * driver implements the V4L2_CID_MIN_BUFFERS_FOR_CAPTURE/OUTPUT > + * control. > * @alloc_devs: &struct device memory type/allocator-specific per-plane device > */ > /* > @@ -622,6 +634,7 @@ struct vb2_queue { > u32 timestamp_flags; > gfp_t gfp_flags; > u32 min_queued_buffers; > + u32 min_reqbufs_allocation; > > struct device *alloc_devs[VB2_MAX_PLANES]; > Thanks, Mauro
Hi Benjamin, On Thu, Mar 14, 2024 at 04:32:19PM +0100, Benjamin Gaignard wrote: > Add 'min_reqbufs_allocation' field in the vb2_queue structure so drivers > can specify the minimum number of buffers to allocate when calling > VIDIOC_REQBUFS. > When initializing the queue, v4l2 core makes sure that the following > constraints are respected: > - the minimum number of buffers to allocate must be at least 2 because > one buffer is used by the hardware while the other is being processed > by userspace. This breaks userspace for the Renesas vsp1 driver :-( Unit tests fail, as some of them rely on operation with a single buffer. The vsp1 is a memory-to-memory processing engine, so operating with a single buffer is fine in some use cases. I would argue that for live capture devices there are valid use cases to operate with a single buffer too. Changing this by default will break use cases. How can we relax this check ? Should I simply submit a patch that lowers the minimum to one buffer ? > -if the driver needs 'min_queued_buffers' in the queue before calling > start_streaming(), then the minimum requirement is 'min_queued_buffers + 1' > to keep at least one buffer available for userspace. > > Simplify __vb2_init_fileio() by using 'min_reqbufs_allocation' directly > to avoid duplicating the minimum number of buffers to allocate computation. > > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com> > --- > .../media/common/videobuf2/videobuf2-core.c | 38 +++++++++++-------- > include/media/videobuf2-core.h | 15 +++++++- > 2 files changed, 37 insertions(+), 16 deletions(-) > > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c > index d8b3c04cb3b5..58c495b253ce 100644 > --- a/drivers/media/common/videobuf2/videobuf2-core.c > +++ b/drivers/media/common/videobuf2/videobuf2-core.c > @@ -866,7 +866,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory, > /* > * Make sure the requested values and current defaults are sane. > */ > - num_buffers = max_t(unsigned int, *count, q->min_queued_buffers); > + num_buffers = max_t(unsigned int, *count, q->min_reqbufs_allocation); > num_buffers = min_t(unsigned int, num_buffers, q->max_num_buffers); > memset(q->alloc_devs, 0, sizeof(q->alloc_devs)); > /* > @@ -918,7 +918,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory, > * There is no point in continuing if we can't allocate the minimum > * number of buffers needed by this vb2_queue. > */ > - if (allocated_buffers < q->min_queued_buffers) > + if (allocated_buffers < q->min_reqbufs_allocation) > ret = -ENOMEM; > > /* > @@ -2524,6 +2524,25 @@ int vb2_core_queue_init(struct vb2_queue *q) > if (WARN_ON(q->supports_requests && q->min_queued_buffers)) > return -EINVAL; > > + /* > + * The minimum requirement is 2: one buffer is used > + * by the hardware while the other is being processed by userspace. > + */ > + if (q->min_reqbufs_allocation < 2) > + q->min_reqbufs_allocation = 2; > + > + /* > + * If the driver needs 'min_queued_buffers' in the queue before > + * calling start_streaming() then the minimum requirement is > + * 'min_queued_buffers + 1' to keep at least one buffer available > + * for userspace. > + */ > + if (q->min_reqbufs_allocation < q->min_queued_buffers + 1) > + q->min_reqbufs_allocation = q->min_queued_buffers + 1; > + > + if (WARN_ON(q->min_reqbufs_allocation > q->max_num_buffers)) > + return -EINVAL; > + > INIT_LIST_HEAD(&q->queued_list); > INIT_LIST_HEAD(&q->done_list); > spin_lock_init(&q->done_lock); > @@ -2717,7 +2736,6 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > struct vb2_fileio_data *fileio; > struct vb2_buffer *vb; > int i, ret; > - unsigned int count = 0; > > /* > * Sanity check > @@ -2738,18 +2756,8 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > if (q->streaming || vb2_get_num_buffers(q) > 0) > return -EBUSY; > > - /* > - * Start with q->min_queued_buffers + 1, driver can increase it in > - * queue_setup() > - * > - * 'min_queued_buffers' buffers need to be queued up before you > - * can start streaming, plus 1 for userspace (or in this case, > - * kernelspace) processing. > - */ > - count = max(2, q->min_queued_buffers + 1); > - > dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n", > - (read) ? "read" : "write", count, q->fileio_read_once, > + (read) ? "read" : "write", q->min_reqbufs_allocation, q->fileio_read_once, > q->fileio_write_immediately); > > fileio = kzalloc(sizeof(*fileio), GFP_KERNEL); > @@ -2763,7 +2771,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > * Request buffers and use MMAP type to force driver > * to allocate buffers by itself. > */ > - fileio->count = count; > + fileio->count = q->min_reqbufs_allocation; > fileio->memory = VB2_MEMORY_MMAP; > fileio->type = q->type; > q->fileio = fileio; > diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h > index 667bf9ee1101..4a8b9135cec8 100644 > --- a/include/media/videobuf2-core.h > +++ b/include/media/videobuf2-core.h > @@ -549,9 +549,21 @@ struct vb2_buf_ops { > * @start_streaming can be called. Used when a DMA engine > * cannot be started unless at least this number of buffers > * have been queued into the driver. > - * VIDIOC_REQBUFS will ensure at least @min_queued_buffers > + * VIDIOC_REQBUFS will ensure at least @min_queued_buffers + 1 > * buffers will be allocated. Note that VIDIOC_CREATE_BUFS will not > * modify the requested buffer count. > + * @min_reqbufs_allocation: the minimum number of buffers to be allocated when > + * calling VIDIOC_REQBUFS. Note that VIDIOC_CREATE_BUFS will *not* > + * modify the requested buffer count and does not use this field. > + * Drivers can set this if there has to be a certain number of > + * buffers available for the hardware to work effectively. > + * This allows calling VIDIOC_REQBUFS with a buffer count of 1 and > + * it will be automatically adjusted to a workable buffer count. > + * If set, then @min_reqbufs_allocation must be larger than > + * @min_queued_buffers + 1. > + * If this field is > 3, then it is highly recommended that the > + * driver implements the V4L2_CID_MIN_BUFFERS_FOR_CAPTURE/OUTPUT > + * control. > * @alloc_devs: &struct device memory type/allocator-specific per-plane device > */ > /* > @@ -622,6 +634,7 @@ struct vb2_queue { > u32 timestamp_flags; > gfp_t gfp_flags; > u32 min_queued_buffers; > + u32 min_reqbufs_allocation; > > struct device *alloc_devs[VB2_MAX_PLANES]; >
Hello, On Thu, Aug 22, 2024 at 08:11:17AM +0200, Hans Verkuil wrote: > On 22/08/2024 03:29, Tomasz Figa wrote: > > On Thu, Aug 22, 2024 at 8:28 AM Laurent Pinchart wrote: > >> On Thu, Mar 14, 2024 at 04:32:19PM +0100, Benjamin Gaignard wrote: > >>> Add 'min_reqbufs_allocation' field in the vb2_queue structure so drivers > >>> can specify the minimum number of buffers to allocate when calling > >>> VIDIOC_REQBUFS. > >>> When initializing the queue, v4l2 core makes sure that the following > >>> constraints are respected: > >>> - the minimum number of buffers to allocate must be at least 2 because > >>> one buffer is used by the hardware while the other is being processed > >>> by userspace. > >> > >> This breaks userspace for the Renesas vsp1 driver :-( Unit tests fail, > >> as some of them rely on operation with a single buffer. > >> > >> The vsp1 is a memory-to-memory processing engine, so operating with a > >> single buffer is fine in some use cases. I would argue that for live > >> capture devices there are valid use cases to operate with a single > >> buffer too. Changing this by default will break use cases. > >> > >> How can we relax this check ? Should I simply submit a patch that lowers > >> the minimum to one buffer ? > >> > > > > Uhm, I didn't notice this when reading this series. (Actually if I > > recall correctly, originally it didn't have this restriction.) > > > > Indeed, I don't see what's wrong with just having 1 buffer. If > > performance is not a concern, it's okay to just serialize the > > operation on 1 buffer. > > > > If you would be so nice to send it, I think a patch that changes > > min_reqbufs_allocation to max(max(1, min_reqbufs_allocation), > > min_queued_buffers)) would be good. > > > > That said, Benjamin, Hans, are we missing something by any chance? :) > > See my proposal below: > > >>> -if the driver needs 'min_queued_buffers' in the queue before calling > >>> start_streaming(), then the minimum requirement is 'min_queued_buffers + 1' > >>> to keep at least one buffer available for userspace. > >>> > >>> Simplify __vb2_init_fileio() by using 'min_reqbufs_allocation' directly > >>> to avoid duplicating the minimum number of buffers to allocate computation. > >>> > >>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com> > >>> --- > >>> .../media/common/videobuf2/videobuf2-core.c | 38 +++++++++++-------- > >>> include/media/videobuf2-core.h | 15 +++++++- > >>> 2 files changed, 37 insertions(+), 16 deletions(-) > >>> > >>> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c > >>> index d8b3c04cb3b5..58c495b253ce 100644 > >>> --- a/drivers/media/common/videobuf2/videobuf2-core.c > >>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c > >>> @@ -866,7 +866,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory, > >>> /* > >>> * Make sure the requested values and current defaults are sane. > >>> */ > >>> - num_buffers = max_t(unsigned int, *count, q->min_queued_buffers); > >>> + num_buffers = max_t(unsigned int, *count, q->min_reqbufs_allocation); > >>> num_buffers = min_t(unsigned int, num_buffers, q->max_num_buffers); > >>> memset(q->alloc_devs, 0, sizeof(q->alloc_devs)); > >>> /* > >>> @@ -918,7 +918,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory, > >>> * There is no point in continuing if we can't allocate the minimum > >>> * number of buffers needed by this vb2_queue. > >>> */ > >>> - if (allocated_buffers < q->min_queued_buffers) > >>> + if (allocated_buffers < q->min_reqbufs_allocation) > >>> ret = -ENOMEM; > >>> > >>> /* > >>> @@ -2524,6 +2524,25 @@ int vb2_core_queue_init(struct vb2_queue *q) > >>> if (WARN_ON(q->supports_requests && q->min_queued_buffers)) > >>> return -EINVAL; > >>> > >>> + /* > >>> + * The minimum requirement is 2: one buffer is used > >>> + * by the hardware while the other is being processed by userspace. > >>> + */ > >>> + if (q->min_reqbufs_allocation < 2) > > This should be: > > if (!q->min_reqbufs_allocation) > > >>> + q->min_reqbufs_allocation = 2; > > and vsp1 should set q->min_reqbufs_allocation to 1. That would work to fix the issue with vsp1, but I don't think it's enough. See below. > >>> + > >>> + /* > >>> + * If the driver needs 'min_queued_buffers' in the queue before > >>> + * calling start_streaming() then the minimum requirement is > >>> + * 'min_queued_buffers + 1' to keep at least one buffer available > >>> + * for userspace. > >>> + */ > >>> + if (q->min_reqbufs_allocation < q->min_queued_buffers + 1) > >>> + q->min_reqbufs_allocation = q->min_queued_buffers + 1; > > The reasoning behind all this is that VIDIOC_REBUFS is expected to allocate > a sane (i.e. workable and efficient) number of buffers. > > So if the DMA engine requires at least X buffers queued, then the minimum > reqbufs allocation is at least q->min_queued_buffers + 1, otherwise you > would never be able to get a buffer back. > > That's also why q->min_reqbufs_allocation was set to a minimum of 2: one > buffer in flight, one buffer processed by userspace. That made the queue_setup > call simpler for quite a few drivers that manually set the buffer count to 2. > For most drivers, allocating 2 buffers makes perfect sense. For devices that can absolutely not work with less than two buffers, setting the minimum to 2 is fine. That is however not the majority use case, and that's why setting the default in the vb2 core, overriding all the drivers that haven't been patched, doesn't sound like a good idea to me. Generally speaking, 2 is in many cases too low. In the common use case of capture and display, you will need a minimum of 3 buffers. Use cases are the responsibility of userspace, we shouldn't try to be too smart here. I actually want to lower the number of buffers and require camera drivers to support operating with a single buffer as a general rule. Drivers that hold on the last buffer until a new one is provided are very painful to use, they're causing issues with libcamera. > But if a driver sets q->min_reqbufs_allocation explicitly to 1, then that > should be honored, and my proposed change above will do that. > > Laurent, if you agree with this, just post patches for this. > > >>> + > >>> + if (WARN_ON(q->min_reqbufs_allocation > q->max_num_buffers)) > >>> + return -EINVAL; > >>> + > >>> INIT_LIST_HEAD(&q->queued_list); > >>> INIT_LIST_HEAD(&q->done_list); > >>> spin_lock_init(&q->done_lock); > >>> @@ -2717,7 +2736,6 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > >>> struct vb2_fileio_data *fileio; > >>> struct vb2_buffer *vb; > >>> int i, ret; > >>> - unsigned int count = 0; > >>> > >>> /* > >>> * Sanity check > >>> @@ -2738,18 +2756,8 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > >>> if (q->streaming || vb2_get_num_buffers(q) > 0) > >>> return -EBUSY; > >>> > >>> - /* > >>> - * Start with q->min_queued_buffers + 1, driver can increase it in > >>> - * queue_setup() > >>> - * > >>> - * 'min_queued_buffers' buffers need to be queued up before you > >>> - * can start streaming, plus 1 for userspace (or in this case, > >>> - * kernelspace) processing. > >>> - */ > >>> - count = max(2, q->min_queued_buffers + 1); > >>> - > >>> dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n", > >>> - (read) ? "read" : "write", count, q->fileio_read_once, > >>> + (read) ? "read" : "write", q->min_reqbufs_allocation, q->fileio_read_once, > >>> q->fileio_write_immediately); > >>> > >>> fileio = kzalloc(sizeof(*fileio), GFP_KERNEL); > >>> @@ -2763,7 +2771,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) > >>> * Request buffers and use MMAP type to force driver > >>> * to allocate buffers by itself. > >>> */ > >>> - fileio->count = count; > >>> + fileio->count = q->min_reqbufs_allocation; > >>> fileio->memory = VB2_MEMORY_MMAP; > >>> fileio->type = q->type; > >>> q->fileio = fileio; > >>> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h > >>> index 667bf9ee1101..4a8b9135cec8 100644 > >>> --- a/include/media/videobuf2-core.h > >>> +++ b/include/media/videobuf2-core.h > >>> @@ -549,9 +549,21 @@ struct vb2_buf_ops { > >>> * @start_streaming can be called. Used when a DMA engine > >>> * cannot be started unless at least this number of buffers > >>> * have been queued into the driver. > >>> - * VIDIOC_REQBUFS will ensure at least @min_queued_buffers > >>> + * VIDIOC_REQBUFS will ensure at least @min_queued_buffers + 1 > >>> * buffers will be allocated. Note that VIDIOC_CREATE_BUFS will not > >>> * modify the requested buffer count. > >>> + * @min_reqbufs_allocation: the minimum number of buffers to be allocated when > >>> + * calling VIDIOC_REQBUFS. Note that VIDIOC_CREATE_BUFS will *not* > >>> + * modify the requested buffer count and does not use this field. > >>> + * Drivers can set this if there has to be a certain number of > >>> + * buffers available for the hardware to work effectively. > >>> + * This allows calling VIDIOC_REQBUFS with a buffer count of 1 and > >>> + * it will be automatically adjusted to a workable buffer count. > >>> + * If set, then @min_reqbufs_allocation must be larger than > >>> + * @min_queued_buffers + 1. > >>> + * If this field is > 3, then it is highly recommended that the > >>> + * driver implements the V4L2_CID_MIN_BUFFERS_FOR_CAPTURE/OUTPUT > >>> + * control. > >>> * @alloc_devs: &struct device memory type/allocator-specific per-plane device > >>> */ > >>> /* > >>> @@ -622,6 +634,7 @@ struct vb2_queue { > >>> u32 timestamp_flags; > >>> gfp_t gfp_flags; > >>> u32 min_queued_buffers; > >>> + u32 min_reqbufs_allocation; > >>> > >>> struct device *alloc_devs[VB2_MAX_PLANES]; > >>>
diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c index d8b3c04cb3b5..58c495b253ce 100644 --- a/drivers/media/common/videobuf2/videobuf2-core.c +++ b/drivers/media/common/videobuf2/videobuf2-core.c @@ -866,7 +866,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory, /* * Make sure the requested values and current defaults are sane. */ - num_buffers = max_t(unsigned int, *count, q->min_queued_buffers); + num_buffers = max_t(unsigned int, *count, q->min_reqbufs_allocation); num_buffers = min_t(unsigned int, num_buffers, q->max_num_buffers); memset(q->alloc_devs, 0, sizeof(q->alloc_devs)); /* @@ -918,7 +918,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory, * There is no point in continuing if we can't allocate the minimum * number of buffers needed by this vb2_queue. */ - if (allocated_buffers < q->min_queued_buffers) + if (allocated_buffers < q->min_reqbufs_allocation) ret = -ENOMEM; /* @@ -2524,6 +2524,25 @@ int vb2_core_queue_init(struct vb2_queue *q) if (WARN_ON(q->supports_requests && q->min_queued_buffers)) return -EINVAL; + /* + * The minimum requirement is 2: one buffer is used + * by the hardware while the other is being processed by userspace. + */ + if (q->min_reqbufs_allocation < 2) + q->min_reqbufs_allocation = 2; + + /* + * If the driver needs 'min_queued_buffers' in the queue before + * calling start_streaming() then the minimum requirement is + * 'min_queued_buffers + 1' to keep at least one buffer available + * for userspace. + */ + if (q->min_reqbufs_allocation < q->min_queued_buffers + 1) + q->min_reqbufs_allocation = q->min_queued_buffers + 1; + + if (WARN_ON(q->min_reqbufs_allocation > q->max_num_buffers)) + return -EINVAL; + INIT_LIST_HEAD(&q->queued_list); INIT_LIST_HEAD(&q->done_list); spin_lock_init(&q->done_lock); @@ -2717,7 +2736,6 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) struct vb2_fileio_data *fileio; struct vb2_buffer *vb; int i, ret; - unsigned int count = 0; /* * Sanity check @@ -2738,18 +2756,8 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) if (q->streaming || vb2_get_num_buffers(q) > 0) return -EBUSY; - /* - * Start with q->min_queued_buffers + 1, driver can increase it in - * queue_setup() - * - * 'min_queued_buffers' buffers need to be queued up before you - * can start streaming, plus 1 for userspace (or in this case, - * kernelspace) processing. - */ - count = max(2, q->min_queued_buffers + 1); - dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n", - (read) ? "read" : "write", count, q->fileio_read_once, + (read) ? "read" : "write", q->min_reqbufs_allocation, q->fileio_read_once, q->fileio_write_immediately); fileio = kzalloc(sizeof(*fileio), GFP_KERNEL); @@ -2763,7 +2771,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) * Request buffers and use MMAP type to force driver * to allocate buffers by itself. */ - fileio->count = count; + fileio->count = q->min_reqbufs_allocation; fileio->memory = VB2_MEMORY_MMAP; fileio->type = q->type; q->fileio = fileio; diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h index 667bf9ee1101..4a8b9135cec8 100644 --- a/include/media/videobuf2-core.h +++ b/include/media/videobuf2-core.h @@ -549,9 +549,21 @@ struct vb2_buf_ops { * @start_streaming can be called. Used when a DMA engine * cannot be started unless at least this number of buffers * have been queued into the driver. - * VIDIOC_REQBUFS will ensure at least @min_queued_buffers + * VIDIOC_REQBUFS will ensure at least @min_queued_buffers + 1 * buffers will be allocated. Note that VIDIOC_CREATE_BUFS will not * modify the requested buffer count. + * @min_reqbufs_allocation: the minimum number of buffers to be allocated when + * calling VIDIOC_REQBUFS. Note that VIDIOC_CREATE_BUFS will *not* + * modify the requested buffer count and does not use this field. + * Drivers can set this if there has to be a certain number of + * buffers available for the hardware to work effectively. + * This allows calling VIDIOC_REQBUFS with a buffer count of 1 and + * it will be automatically adjusted to a workable buffer count. + * If set, then @min_reqbufs_allocation must be larger than + * @min_queued_buffers + 1. + * If this field is > 3, then it is highly recommended that the + * driver implements the V4L2_CID_MIN_BUFFERS_FOR_CAPTURE/OUTPUT + * control. * @alloc_devs: &struct device memory type/allocator-specific per-plane device */ /* @@ -622,6 +634,7 @@ struct vb2_queue { u32 timestamp_flags; gfp_t gfp_flags; u32 min_queued_buffers; + u32 min_reqbufs_allocation; struct device *alloc_devs[VB2_MAX_PLANES];
Add 'min_reqbufs_allocation' field in the vb2_queue structure so drivers can specify the minimum number of buffers to allocate when calling VIDIOC_REQBUFS. When initializing the queue, v4l2 core makes sure that the following constraints are respected: - the minimum number of buffers to allocate must be at least 2 because one buffer is used by the hardware while the other is being processed by userspace. -if the driver needs 'min_queued_buffers' in the queue before calling start_streaming(), then the minimum requirement is 'min_queued_buffers + 1' to keep at least one buffer available for userspace. Simplify __vb2_init_fileio() by using 'min_reqbufs_allocation' directly to avoid duplicating the minimum number of buffers to allocate computation. Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com> --- .../media/common/videobuf2/videobuf2-core.c | 38 +++++++++++-------- include/media/videobuf2-core.h | 15 +++++++- 2 files changed, 37 insertions(+), 16 deletions(-)