[Linaro-mm-sig] Re: [PATCH v3 04/11] iio: buffer-dma: Enable buffer write support

On Mon, 3 Apr 2023 17:47:53 +0200 Paul Cercueil paul@crapouillou.net wrote:

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).

As they are doing the same thing, I'd like that to be visible down where the callback is set. As such, do we need a wrapper to provide the space available version? Perhaps just give the data_available version a more generic name to make it seem appropriate for both usecases?

Otherwise LGTM.

Jonathan

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

---

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()

v3: - Reorganize arguments to iio_dma_buffer_io() - Change 'is_write' argument to 'is_from_user' - Change (__force char *) to (__force __user char *), in iio_dma_buffer_write(), since we only want to drop the "const".

---

drivers/iio/buffer/industrialio-buffer-dma.c | 89 ++++++++++++++++---- include/linux/iio/buffer-dma.h | 7 ++ 2 files changed, 80 insertions(+), 16 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c index 1fc91467d1aa..86eced458236 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_from_user)
  

{ 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_from_user)

• 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 +546,40 @@ 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 __user 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);

As mentioned above, I don't see having this trivial wrapper as beneficial.

+}

#endif