Re: [PATCH v6 08/17] iio: buffer-dmaengine: split requesting DMA channel from allocating buffer

[Nuno Sá <noname.nuno@xxxxxxxxx>]

On Wed, 2024-12-11 at 14:54 -0600, David Lechner wrote:
> Refactor the IIO dmaengine buffer code to split requesting the DMA
> channel from allocating the buffer. We want to be able to add a new
> function where the IIO device driver manages the DMA channel, so these
> two actions need to be separate.
> 
> To do this, calling dma_request_chan() is moved from
> iio_dmaengine_buffer_alloc() to iio_dmaengine_buffer_setup_ext(). A new
> __iio_dmaengine_buffer_setup_ext() helper function is added to simplify
> error unwinding and will also be used by a new function in a later
> patch.
> 
> iio_dmaengine_buffer_free() now only frees the buffer and does not
> release the DMA channel. A new iio_dmaengine_buffer_teardown() function
> is added to unwind everything done in iio_dmaengine_buffer_setup_ext().
> This keeps things more symmetrical with obvious pairs alloc/free and
> setup/teardown.
> 
> Calling dma_get_slave_caps() in iio_dmaengine_buffer_alloc() is moved so
> that we can avoid any gotos for error unwinding.
> 
> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
> ---

Reviewed-by: Nuno Sa <nuno.sa@xxxxxxxxxx>

> 
> v6 changes:
> * Split out from patch that adds the new function
> * Dropped owns_chan flag
> * Introduced iio_dmaengine_buffer_teardown() so that
>   iio_dmaengine_buffer_free() doesn't have to manage the DMA channel
> ---
>  drivers/iio/adc/adi-axi-adc.c                      |   2 +-
>  drivers/iio/buffer/industrialio-buffer-dmaengine.c | 106 ++++++++++++--------
> -
>  drivers/iio/dac/adi-axi-dac.c                      |   2 +-
>  include/linux/iio/buffer-dmaengine.h               |   2 +-
>  4 files changed, 65 insertions(+), 47 deletions(-)
> 
> diff --git a/drivers/iio/adc/adi-axi-adc.c b/drivers/iio/adc/adi-axi-adc.c
> index
> c7357601f0f869e57636f00bb1e26c059c3ab15c..a55db308baabf7b26ea98431cab1e6af7fe2
> a5f3 100644
> --- a/drivers/iio/adc/adi-axi-adc.c
> +++ b/drivers/iio/adc/adi-axi-adc.c
> @@ -305,7 +305,7 @@ static struct iio_buffer *axi_adc_request_buffer(struct
> iio_backend *back,
>  static void axi_adc_free_buffer(struct iio_backend *back,
>  				struct iio_buffer *buffer)
>  {
> -	iio_dmaengine_buffer_free(buffer);
> +	iio_dmaengine_buffer_teardown(buffer);
>  }
>  
>  static int axi_adc_reg_access(struct iio_backend *back, unsigned int reg,
> diff --git a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> index
> 614e1c4189a9cdd5a8d9d8c5ef91566983032951..02847d3962fcbb43ec76167db6482ab951f2
> 0942 100644
> --- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> +++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> @@ -206,39 +206,29 @@ static const struct iio_dev_attr
> *iio_dmaengine_buffer_attrs[] = {
>  
>  /**
>   * iio_dmaengine_buffer_alloc() - Allocate new buffer which uses DMAengine
> - * @dev: DMA channel consumer device
> - * @channel: DMA channel name, typically "rx".
> + * @chan: DMA channel.
>   *
>   * This allocates a new IIO buffer which internally uses the DMAengine
> framework
> - * to perform its transfers. The parent device will be used to request the
> DMA
> - * channel.
> + * to perform its transfers.
>   *
>   * Once done using the buffer iio_dmaengine_buffer_free() should be used to
>   * release it.
>   */
> -static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
> -	const char *channel)
> +static struct iio_buffer *iio_dmaengine_buffer_alloc(struct dma_chan *chan)
>  {
>  	struct dmaengine_buffer *dmaengine_buffer;
>  	unsigned int width, src_width, dest_width;
>  	struct dma_slave_caps caps;
> -	struct dma_chan *chan;
>  	int ret;
>  
> +	ret = dma_get_slave_caps(chan, &caps);
> +	if (ret < 0)
> +		return ERR_PTR(ret);
> +
>  	dmaengine_buffer = kzalloc(sizeof(*dmaengine_buffer), GFP_KERNEL);
>  	if (!dmaengine_buffer)
>  		return ERR_PTR(-ENOMEM);
>  
> -	chan = dma_request_chan(dev, channel);
> -	if (IS_ERR(chan)) {
> -		ret = PTR_ERR(chan);
> -		goto err_free;
> -	}
> -
> -	ret = dma_get_slave_caps(chan, &caps);
> -	if (ret < 0)
> -		goto err_release;
> -
>  	/* Needs to be aligned to the maximum of the minimums */
>  	if (caps.src_addr_widths)
>  		src_width = __ffs(caps.src_addr_widths);
> @@ -262,12 +252,6 @@ static struct iio_buffer
> *iio_dmaengine_buffer_alloc(struct device *dev,
>  	dmaengine_buffer->queue.buffer.access = &iio_dmaengine_buffer_ops;
>  
>  	return &dmaengine_buffer->queue.buffer;
> -
> -err_release:
> -	dma_release_channel(chan);
> -err_free:
> -	kfree(dmaengine_buffer);
> -	return ERR_PTR(ret);
>  }
>  
>  /**
> @@ -276,17 +260,57 @@ static struct iio_buffer
> *iio_dmaengine_buffer_alloc(struct device *dev,
>   *
>   * Frees a buffer previously allocated with iio_dmaengine_buffer_alloc().
>   */
> -void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
> +static void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
>  {
>  	struct dmaengine_buffer *dmaengine_buffer =
>  		iio_buffer_to_dmaengine_buffer(buffer);
>  
>  	iio_dma_buffer_exit(&dmaengine_buffer->queue);
> -	dma_release_channel(dmaengine_buffer->chan);
> -
>  	iio_buffer_put(buffer);
>  }
> -EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_free, "IIO_DMAENGINE_BUFFER");
> +
> +/**
> + * iio_dmaengine_buffer_teardown() - Releases DMA channel and frees buffer
> + * @buffer: Buffer to free
> + *
> + * Releases the DMA channel and frees the buffer previously setup with
> + * iio_dmaengine_buffer_setup_ext().
> + */
> +void iio_dmaengine_buffer_teardown(struct iio_buffer *buffer)
> +{
> +	struct dmaengine_buffer *dmaengine_buffer =
> +		iio_buffer_to_dmaengine_buffer(buffer);
> +	struct dma_chan *chan = dmaengine_buffer->chan;
> +
> +	iio_dmaengine_buffer_free(buffer);
> +	dma_release_channel(chan);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_teardown, "IIO_DMAENGINE_BUFFER");
> +
> +static struct iio_buffer
> +*__iio_dmaengine_buffer_setup_ext(struct iio_dev *indio_dev,
> +				  struct dma_chan *chan,
> +				  enum iio_buffer_direction dir)
> +{
> +	struct iio_buffer *buffer;
> +	int ret;
> +
> +	buffer = iio_dmaengine_buffer_alloc(chan);
> +	if (IS_ERR(buffer))
> +		return ERR_CAST(buffer);
> +
> +	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
> +
> +	buffer->direction = dir;
> +
> +	ret = iio_device_attach_buffer(indio_dev, buffer);
> +	if (ret) {
> +		iio_dmaengine_buffer_free(buffer);
> +		return ERR_PTR(ret);
> +	}
> +
> +	return buffer;
> +}
>  
>  /**
>   * iio_dmaengine_buffer_setup_ext() - Setup a DMA buffer for an IIO device
> @@ -300,7 +324,7 @@ EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_free,
> "IIO_DMAENGINE_BUFFER");
>   * It also appends the INDIO_BUFFER_HARDWARE mode to the supported modes of
> the
>   * IIO device.
>   *
> - * Once done using the buffer iio_dmaengine_buffer_free() should be used to
> + * Once done using the buffer iio_dmaengine_buffer_teardown() should be used
> to
>   * release it.
>   */
>  struct iio_buffer *iio_dmaengine_buffer_setup_ext(struct device *dev,
> @@ -308,30 +332,24 @@ struct iio_buffer *iio_dmaengine_buffer_setup_ext(struct
> device *dev,
>  						  const char *channel,
>  						  enum iio_buffer_direction
> dir)
>  {
> +	struct dma_chan *chan;
>  	struct iio_buffer *buffer;
> -	int ret;
> -
> -	buffer = iio_dmaengine_buffer_alloc(dev, channel);
> -	if (IS_ERR(buffer))
> -		return ERR_CAST(buffer);
> -
> -	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
>  
> -	buffer->direction = dir;
> +	chan = dma_request_chan(dev, channel);
> +	if (IS_ERR(chan))
> +		return ERR_CAST(chan);
>  
> -	ret = iio_device_attach_buffer(indio_dev, buffer);
> -	if (ret) {
> -		iio_dmaengine_buffer_free(buffer);
> -		return ERR_PTR(ret);
> -	}
> +	buffer = __iio_dmaengine_buffer_setup_ext(indio_dev, chan, dir);
> +	if (IS_ERR(buffer))
> +		dma_release_channel(chan);
>  
>  	return buffer;
>  }
>  EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_setup_ext, "IIO_DMAENGINE_BUFFER");
>  
> -static void __devm_iio_dmaengine_buffer_free(void *buffer)
> +static void devm_iio_dmaengine_buffer_teardown(void *buffer)
>  {
> -	iio_dmaengine_buffer_free(buffer);
> +	iio_dmaengine_buffer_teardown(buffer);
>  }
>  
>  /**
> @@ -357,7 +375,7 @@ int devm_iio_dmaengine_buffer_setup_ext(struct device
> *dev,
>  	if (IS_ERR(buffer))
>  		return PTR_ERR(buffer);
>  
> -	return devm_add_action_or_reset(dev,
> __devm_iio_dmaengine_buffer_free,
> +	return devm_add_action_or_reset(dev,
> devm_iio_dmaengine_buffer_teardown,
>  					buffer);
>  }
>  EXPORT_SYMBOL_NS_GPL(devm_iio_dmaengine_buffer_setup_ext,
> "IIO_DMAENGINE_BUFFER");
> diff --git a/drivers/iio/dac/adi-axi-dac.c b/drivers/iio/dac/adi-axi-dac.c
> index
> b143f7ed6847277aeb49094627d90e5d95eed71c..5d5157af0a233143daff906b699bdae10f36
> 8867 100644
> --- a/drivers/iio/dac/adi-axi-dac.c
> +++ b/drivers/iio/dac/adi-axi-dac.c
> @@ -168,7 +168,7 @@ static struct iio_buffer *axi_dac_request_buffer(struct
> iio_backend *back,
>  static void axi_dac_free_buffer(struct iio_backend *back,
>  				struct iio_buffer *buffer)
>  {
> -	iio_dmaengine_buffer_free(buffer);
> +	iio_dmaengine_buffer_teardown(buffer);
>  }
>  
>  enum {
> diff --git a/include/linux/iio/buffer-dmaengine.h b/include/linux/iio/buffer-
> dmaengine.h
> index
> 81d9a19aeb9199dd58bb9d35a91f0ec4b00846df..72a2e3fd8a5bf5e8f27ee226ddd92979d233
> 754b 100644
> --- a/include/linux/iio/buffer-dmaengine.h
> +++ b/include/linux/iio/buffer-dmaengine.h
> @@ -12,7 +12,7 @@
>  struct iio_dev;
>  struct device;
>  
> -void iio_dmaengine_buffer_free(struct iio_buffer *buffer);
> +void iio_dmaengine_buffer_teardown(struct iio_buffer *buffer);
>  struct iio_buffer *iio_dmaengine_buffer_setup_ext(struct device *dev,
>  						  struct iio_dev *indio_dev,
>  						  const char *channel,
>