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

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 21 Nov 2021 17:19:32 +0000
Paul Cercueil <paul@crapouillou.net> wrote:

> Hi Jonathan,
> 
> Le dim., nov. 21 2021 at 14:20:49 +0000, Jonathan Cameron 
> <jic23@kernel.org> a écrit :
> > 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?  
> 
> When using an input buffer the block->bytes_used is unconditionally 
> reset in iio_dmaengine_buffer_submit_block(), so this was fine until 
> now.
> 
> When using an output buffer the block->bytes_used can actually (with 
> the new API) be specified by the user, so we don't want 
> iio_dmaengine_buffer_submit_block() to unconditionally override it. 
> Which means that in the case where we have an output buffer in fileio 
> mode, we do need block->bytes_used to be initialized to the buffer's 
> size since it won't be set anywhere else.

Makes sense.  Thanks for the explanation.

> 
> About the change in block->state: in patch [01/15] we removed the 
> incoming/outgoing queues, and while the "enqueued" state is still 
> useful to know which buffers have to be submitted when the buffer is 
> enabled, the "dequeued" state is not useful anymore since there is no 
> more distinction vs. the "done" state.
> 
> I believe this change should be moved to patch [01/15] then, and I 
> should go further and remove the IIO_BLOCK_STATE_DEQUEUED completely.

Complete removal would indeed be a more 'obvious' change, so I'd support
that assuming now disadvantages we havent' thought of yet.
> 
> >>   	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.  
> 
> Ok.
> 
> >>   	}
> >> 
> >>   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.  
> 
> Right.
> 
> >>  +	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.  
> 
> See the explanation above. Although I most likely don't need to set it 
> at two different spots... I'll check that in detail next week.
> 
> Cheers,
> -Paul
> 
> >>   		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  
> >   
> 
>