[PATCH v2 02/12] iio: buffer-dma: Enable buffer write support

Paul Cercueil
2022-02-07T13:16:54Z

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.

The .space_available() callback can return the exact same value as the
.data_available() callback for input buffers, since in both cases we
count the exact same thing (the number of bytes in each available
block).

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.

v2: - Fix block->state not being reset in
iio_dma_buffer_request_update() for output buffers.
- Only update block->bytes_used once and add a comment about why we
update it.
- Add a comment about why we're setting a different state for output
buffers in iio_dma_buffer_request_update()
- Remove useless cast to bool (!!) in iio_dma_buffer_io()

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
---
drivers/iio/buffer/industrialio-buffer-dma.c | 88 ++++++++++++++++----
include/linux/iio/buffer-dma.h | 7 ++
2 files changed, 79 insertions(+), 16 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c
index 1fc91467d1aa..a9f1b673374f 100644
--- a/drivers/iio/buffer/industrialio-buffer-dma.c
+++ b/drivers/iio/buffer/industrialio-buffer-dma.c
@@ -195,6 +195,18 @@ static void _iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
block->state = IIO_BLOCK_STATE_DONE;
}

+static void iio_dma_buffer_queue_wake(struct iio_dma_buffer_queue *queue)
+{
+ __poll_t flags;
+
+ if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN)
+ flags = EPOLLIN | EPOLLRDNORM;
+ else
+ flags = EPOLLOUT | EPOLLWRNORM;
+
+ wake_up_interruptible_poll(&queue->buffer.pollq, flags);
+}
+
/**
* iio_dma_buffer_block_done() - Indicate that a block has been completed
* @block: The completed block
@@ -212,7 +224,7 @@ void iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
spin_unlock_irqrestore(&queue->list_lock, flags);

iio_buffer_block_put_atomic(block);
- wake_up_interruptible_poll(&queue->buffer.pollq, EPOLLIN | EPOLLRDNORM);
+ iio_dma_buffer_queue_wake(queue);
}
EXPORT_SYMBOL_GPL(iio_dma_buffer_block_done);

@@ -241,7 +253,7 @@ void iio_dma_buffer_block_list_abort(struct iio_dma_buffer_queue *queue,
}
spin_unlock_irqrestore(&queue->list_lock, flags);

- wake_up_interruptible_poll(&queue->buffer.pollq, EPOLLIN | EPOLLRDNORM);
+ iio_dma_buffer_queue_wake(queue);
}
EXPORT_SYMBOL_GPL(iio_dma_buffer_block_list_abort);

@@ -335,8 +347,24 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)
queue->fileio.blocks[i] = block;
}

- block->state = IIO_BLOCK_STATE_QUEUED;
- list_add_tail(&block->head, &queue->incoming);
+ /*
+ * block->bytes_used may have been modified previously, e.g. by
+ * iio_dma_buffer_block_list_abort(). Reset it here to the
+ * block's so that iio_dma_buffer_io() will work.
+ */
+ block->bytes_used = block->size;
+
+ /*
+ * If it's an input buffer, mark the block as queued, and
+ * iio_dma_buffer_enable() will submit it. Otherwise mark it as
+ * done, which means it's ready to be dequeued.
+ */
+ if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN) {
+ block->state = IIO_BLOCK_STATE_QUEUED;
+ list_add_tail(&block->head, &queue->incoming);
+ } else {
+ block->state = IIO_BLOCK_STATE_DONE;
+ }
}

out_unlock:
@@ -465,20 +493,12 @@ static struct iio_dma_buffer_block *iio_dma_buffer_dequeue(
return block;
}

-/**
- * iio_dma_buffer_read() - DMA buffer read callback
- * @buffer: Buffer to read form
- * @n: Number of bytes to read
- * @user_buffer: Userspace buffer to copy the data to
- *
- * Should be used as the read callback for iio_buffer_access_ops
- * struct for DMA buffers.
- */
-int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
- char __user *user_buffer)
+static int iio_dma_buffer_io(struct iio_buffer *buffer,
+ size_t n, char __user *user_buffer, bool is_write)
{
struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
struct iio_dma_buffer_block *block;
+ void *addr;
int ret;

if (n < buffer->bytes_per_datum)
@@ -501,8 +521,13 @@ int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
n = rounddown(n, buffer->bytes_per_datum);
if (n > block->bytes_used - queue->fileio.pos)
n = block->bytes_used - queue->fileio.pos;
+ addr = block->vaddr + queue->fileio.pos;

- if (copy_to_user(user_buffer, block->vaddr + queue->fileio.pos, n)) {
+ if (is_write)
+ ret = copy_from_user(addr, user_buffer, n);
+ else
+ ret = copy_to_user(user_buffer, addr, n);
+ if (ret) {
ret = -EFAULT;
goto out_unlock;
}
@@ -521,8 +546,39 @@ int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,

return ret;
}
+
+/**
+ * iio_dma_buffer_read() - DMA buffer read callback
+ * @buffer: Buffer to read form
+ * @n: Number of bytes to read
+ * @user_buffer: Userspace buffer to copy the data to
+ *
+ * Should be used as the read callback for iio_buffer_access_ops
+ * struct for DMA buffers.
+ */
+int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
+ char __user *user_buffer)
+{
+ return iio_dma_buffer_io(buffer, n, user_buffer, false);
+}
EXPORT_SYMBOL_GPL(iio_dma_buffer_read);

+/**
+ * iio_dma_buffer_write() - DMA buffer write callback
+ * @buffer: Buffer to read form
+ * @n: Number of bytes to read
+ * @user_buffer: Userspace buffer to copy the data from
+ *
+ * Should be used as the write callback for iio_buffer_access_ops
+ * struct for DMA buffers.
+ */
+int iio_dma_buffer_write(struct iio_buffer *buffer, size_t n,
+ const char __user *user_buffer)
+{
+ return iio_dma_buffer_io(buffer, n, (__force char *)user_buffer, true);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_write);
+
/**
* iio_dma_buffer_data_available() - DMA buffer data_available callback
* @buf: Buffer to check for data availability
diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h
index 18d3702fa95d..490b93f76fa8 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_data_available(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);
@@ -142,4 +144,9 @@ int iio_dma_buffer_init(struct iio_dma_buffer_queue *queue,
void iio_dma_buffer_exit(struct iio_dma_buffer_queue *queue);
void iio_dma_buffer_release(struct iio_dma_buffer_queue *queue);

+static inline size_t iio_dma_buffer_space_available(struct iio_buffer *buffer)
+{
+ return iio_dma_buffer_data_available(buffer);
+}
+
#endif
--
2.34.1