On Wed, 5 Jun 2024 13:08:42 +0200
Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:
> Add the necessary infrastructure to the IIO core to support a new
> optional DMABUF based interface.
>
> With this new interface, DMABUF objects (externally created) can be
> attached to a IIO buffer, and subsequently used for data transfer.
>
> A userspace application can then use this interface to share DMABUF
> objects between several interfaces, allowing it to transfer data in a
> zero-copy fashion, for instance between IIO and the USB stack.
>
> The userspace application can also memory-map the DMABUF objects, and
> access the sample data directly. The advantage of doing this vs. the
> read() interface is that it avoids an extra copy of the data between the
> kernel and userspace. This is particularly userful for high-speed
> devices which produce several megabytes or even gigabytes of data per
> second.
>
> As part of the interface, 3 new IOCTLs have been added:
>
> IIO_BUFFER_DMABUF_ATTACH_IOCTL(int fd):
> Attach the DMABUF object identified by the given file descriptor to the
> buffer.
>
> IIO_BUFFER_DMABUF_DETACH_IOCTL(int fd):
> Detach the DMABUF object identified by the given file descriptor from
> the buffer. Note that closing the IIO buffer's file descriptor will
> automatically detach all previously attached DMABUF objects.
>
> IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *):
> Request a data transfer to/from the given DMABUF object. Its file
> descriptor, as well as the transfer size and flags are provided in the
> "iio_dmabuf" structure.
>
> These three IOCTLs have to be performed on the IIO buffer's file
> descriptor, obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
>
> Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> Signed-off-by: Nuno Sa <nuno.sa@xxxxxxxxxx>
Need a brief note on the sign off chain.
What is Nuno's role in this series as he's not sending the emails and not
marked with Co-developed-by
I gave this a much more thorough look in earlier versions than I have today but
a few really minor things inline (that I might have fixed up whilst applying)
but looks like you'll be done a v11 for Randy's docs comments anyway :(
Jonathan
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 0138b21b244f..c98c8ac83785 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> +struct iio_dmabuf_priv {
> + struct list_head entry;
> + struct kref ref;
> +
> + struct iio_buffer *buffer;
> + struct iio_dma_buffer_block *block;
> +
> + u64 context;
> + spinlock_t lock;
Given you are going to have a v11, please add a comment to this lock
to say what data it is protecting.
> +
> + struct dma_buf_attachment *attach;
> + struct sg_table *sgt;
> + enum dma_data_direction dir;
> + atomic_t seqno;
> +};
> diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
> index 89c3fd7c29ca..1a221c1d7736 100644
> --- a/include/linux/iio/buffer_impl.h
> +++ b/include/linux/iio/buffer_impl.h
> @@ -9,8 +9,12 @@
> #include <uapi/linux/iio/buffer.h>
> #include <linux/iio/buffer.h>
>
> +struct dma_buf_attachment;
> +struct dma_fence;
> struct iio_dev;
> +struct iio_dma_buffer_block;
> struct iio_buffer;
> +struct sg_table;
>
> /**
> * INDIO_BUFFER_FLAG_FIXED_WATERMARK - Watermark level of the buffer can not be
> @@ -39,6 +43,13 @@ struct iio_buffer;
> * device stops sampling. Calles are balanced with @enable.
> * @release: called when the last reference to the buffer is dropped,
> * should free all resources allocated by the buffer.
> + * @attach_dmabuf: called from userspace via ioctl to attach one external
> + * DMABUF.
> + * @detach_dmabuf: called from userspace via ioctl to detach one previously
> + * attached DMABUF.
> + * @enqueue_dmabuf: called from userspace via ioctl to queue this DMABUF
> + * object to this buffer. Requires a valid DMABUF fd, that
> + * was previouly attached to this buffer.
Missing docs for lock_queue() and unlock_queue()
Kernel-doc must be complete or bots are going to moan at us :(
> * @modes: Supported operating modes by this buffer type
> * @flags: A bitmask combination of INDIO_BUFFER_FLAG_*
> *
> @@ -68,6 +79,17 @@ struct iio_buffer_access_funcs {
>
> void (*release)(struct iio_buffer *buffer);
>
> + struct iio_dma_buffer_block * (*attach_dmabuf)(struct iio_buffer *buffer,
> + struct dma_buf_attachment *attach);
> + void (*detach_dmabuf)(struct iio_buffer *buffer,
> + struct iio_dma_buffer_block *block);
> + int (*enqueue_dmabuf)(struct iio_buffer *buffer,
> + struct iio_dma_buffer_block *block,
> + struct dma_fence *fence, struct sg_table *sgt,
> + size_t size, bool cyclic);
> + void (*lock_queue)(struct iio_buffer *buffer);
> + void (*unlock_queue)(struct iio_buffer *buffer);
> +
