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

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 11 Dec 2024 14:54:45 -0600
David Lechner <dlechner@baylibre.com> 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@baylibre.com>
> ---
> 
> 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

Ouch this is a fiddly refactor to unwind from the diff.
I 'think' it's correct, but am keen to get a few more eyes on this
if possible.  Not 100% sure what route this series will take, so on off
chance this patch doesn't go through IIO or a immutable branch I
create.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>