Re: [PATCH RFC v3 7/9] iio: buffer-dmaengine: generalize requesting DMA channel

[Jonathan Cameron <jic23@xxxxxxxxxx>]

On Mon, 22 Jul 2024 16:57:14 -0500
David Lechner <dlechner@xxxxxxxxxxxx> wrote:

> This patch generalizes the iio_dmaengine_buffer_setup_ext() functions
> by passing the pointer to the DMA channel as an argument rather than
> the channel name. This will allow future callers of the function to
> use other methods to get the DMA channel pointer.
> 
> This aims to keep it as easy to use as possible by stealing ownership
> of the dma_chan pointer from the caller. This way, dma_request_chan()
> can be called inline in the function call without any extra error
> handling.

That's odd enough to be a likely source of future bugs. Doesn't seem
necessary to me. Just have the extra handling in the few places it's needed.

Or add a wrapper for this case where you just provide the
channel name as was done before this patch.

> 
> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
> 
> v3 changes:
> * This is a new patch in v3.


...

> @@ -277,22 +282,26 @@ static void __devm_iio_dmaengine_buffer_free(void *buffer)
>   * devm_iio_dmaengine_buffer_setup_ext() - Setup a DMA buffer for an IIO device
>   * @dev: Parent device for the buffer
>   * @indio_dev: IIO device to which to attach this buffer.
> - * @channel: DMA channel name, typically "rx".
> + * @chan: DMA channel.
>   * @dir: Direction of buffer (in or out)
>   *
>   * This allocates a new IIO buffer with devm_iio_dmaengine_buffer_alloc()
>   * and attaches it to an IIO device with iio_device_attach_buffer().
>   * It also appends the INDIO_BUFFER_HARDWARE mode to the supported modes of the
>   * IIO device.
> + *
> + * This "steals" the @chan pointer, so the caller must not call
> + * dma_release_channel() on it. @chan is also checked for error, so callers
> + * can pass the result of dma_request_chan() directly.
>   */
>  int devm_iio_dmaengine_buffer_setup_ext(struct device *dev,
>  					struct iio_dev *indio_dev,
> -					const char *channel,
> +					struct dma_chan *chan,
>  					enum iio_buffer_direction dir)
>  {
>  	struct iio_buffer *buffer;
>  
> -	buffer = iio_dmaengine_buffer_setup_ext(dev, indio_dev, channel, dir);
> +	buffer = iio_dmaengine_buffer_setup_ext(dev, indio_dev, chan, dir);
>  	if (IS_ERR(buffer))
>  		return PTR_ERR(buffer);
>