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

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Message-ID: <20241214143745.681e8408@jic23-huawei>
Date: Sat, 14 Dec 2024 14:37:45 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Nuno Sá <nuno.sa@...log.com>, Uwe
 Kleine-König <ukleinek@...nel.org>, Michael Hennerich
 <Michael.Hennerich@...log.com>, Lars-Peter Clausen <lars@...afoo.de>, David
 Jander <david@...tonic.nl>, Martin Sperl <kernel@...tin.sperl.org>,
 linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
 linux-pwm@...r.kernel.org
Subject: Re: [PATCH v6 08/17] iio: buffer-dmaengine: split requesting DMA
 channel from allocating buffer

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