iio: buffer-dma: Enable buffer write support

Adding write support to the buffer-dma code is easy - the write()
function basically needs to do the exact same thing as the read()
function: dequeue a block, read or write the data, enqueue the block
when entirely processed.

Therefore, the iio_buffer_dma_read() and the new iio_buffer_dma_write()
now both call a function iio_buffer_dma_io(), which will perform this
task.

Note that we preemptively reset block->bytes_used to the buffer's size
in iio_dma_buffer_request_update(), as in the future the
iio_dma_buffer_enqueue() function won't reset it.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240419-iio-backend-axi-dac-v4-3-5ca45b4de294@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h
index 52a838ec0e57..6e27e47077d5 100644
--- a/include/linux/iio/buffer-dma.h
+++ b/include/linux/iio/buffer-dma.h
@@ -132,6 +132,8 @@ int iio_dma_buffer_disable(struct iio_buffer *buffer,
 	struct iio_dev *indio_dev);
 int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
 	char __user *user_buffer);
+int iio_dma_buffer_write(struct iio_buffer *buffer, size_t n,
+			 const char __user *user_buffer);
 size_t iio_dma_buffer_usage(struct iio_buffer *buffer);
 int iio_dma_buffer_set_bytes_per_datum(struct iio_buffer *buffer, size_t bpd);
 int iio_dma_buffer_set_length(struct iio_buffer *buffer, unsigned int length);