iio: core: Add new DMABUF interface infrastructure

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@crapouillou.net>
Co-developed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240620122726.41232-4-paul@crapouillou.net
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
index 89c3fd7c29ca..e72552e026f3 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 +43,16 @@ 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.
+ * @lock_queue:		called when the core needs to lock the buffer queue;
+ *                      it is used when enqueueing DMABUF objects.
+ * @unlock_queue:       used to unlock a previously locked buffer queue
  * @modes:		Supported operating modes by this buffer type
  * @flags:		A bitmask combination of INDIO_BUFFER_FLAG_*
  *
@@ -68,6 +82,17 @@ 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);
+
 	unsigned int modes;
 	unsigned int flags;
 };
@@ -136,6 +161,12 @@ struct iio_buffer {
 
 	/* @ref: Reference count of the buffer. */
 	struct kref ref;
+
+	/* @dmabufs: List of DMABUF attachments */
+	struct list_head dmabufs; /* P: dmabufs_mutex */
+
+	/* @dmabufs_mutex: Protects dmabufs */
+	struct mutex dmabufs_mutex;
 };
 
 /**
@@ -159,6 +190,8 @@ void iio_buffer_init(struct iio_buffer *buffer);
 struct iio_buffer *iio_buffer_get(struct iio_buffer *buffer);
 void iio_buffer_put(struct iio_buffer *buffer);
 
+void iio_buffer_signal_dmabuf_done(struct dma_fence *fence, int ret);
+
 #else /* CONFIG_IIO_BUFFER */
 
 static inline void iio_buffer_get(struct iio_buffer *buffer) {}