Re: [PATCH 04/15] iio: buffer-dma: Enable buffer write support

On Mon, 15 Nov 2021 14:19:14 +0000 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).

Signed-off-by: Paul Cercueil paul@crapouillou.net

Hi Paul,

There are a few changes in here, such as the bytes_used value being set that I'm not following the reasoning behind. More info on those? Also good to provide something about those in this patch description.

Thanks,

Jonathan

---

drivers/iio/buffer/industrialio-buffer-dma.c | 75 +++++++++++++++----- include/linux/iio/buffer-dma.h | 7 ++ 2 files changed, 66 insertions(+), 16 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c index abac88f20104..eeeed6b2e0cf 100644 --- a/drivers/iio/buffer/industrialio-buffer-dma.c +++ b/drivers/iio/buffer/industrialio-buffer-dma.c @@ -179,7 +179,8 @@ static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block( }

block->size = size;

• block->state = IIO_BLOCK_STATE_DEQUEUED;

• block->bytes_used = size;
• block->state = IIO_BLOCK_STATE_DONE;

I don't know why these are here - some more info?

block->queue = queue; INIT_LIST_HEAD(&block->head); kref_init(&block->kref); @@ -195,6 +196,18 @@ 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 +225,7 @@ 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 +254,7 @@ 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);

@@ -334,7 +347,8 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer) queue->fileio.blocks[i] = block; }

• block->state = IIO_BLOCK_STATE_QUEUED;
  

• if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN)
  

• 	block->state = IIO_BLOCK_STATE_QUEUED;
  

Possibly worth a comment on the state being set here. I figured it out, but might save some brain cells in future if it's stated in the code.

}

out_unlock: @@ -467,20 +481,12 @@ 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)

@@ -503,8 +509,13 @@ 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);
  

What is the !! gaining us here? We only care about == 0 vs != 0 so forcing it to be 0 or 1 isn't useful.

• if (ret) { ret = -EFAULT; goto out_unlock; }

@@ -513,6 +524,7 @@ int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,

if (queue->fileio.pos == block->bytes_used) { queue->fileio.active_block = NULL;

• block->bytes_used = block->size;
  

This seems to be a functional change that isn't called out in the patch description.

iio_dma_buffer_enqueue(queue, block);

}

@@ -523,8 +535,39 @@ 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 a65a005c4a19..09c07d5563c0 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