linux-kernel - Re: [PATCH v2 1/4] dma: Add devm_dma_request

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Message-ID: <20250203-chalice-ninth-8235590e29d2@thorsis.com>
Date: Mon, 3 Feb 2025 13:27:02 +0100
From: Alexander Dahl <ada@...rsis.com>
To: Bence Csókás <csokas.bence@...lan.hu>
Cc: dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nel.org>, Vinod Koul <vkoul@...nel.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>, linux-spi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 1/4] dma: Add devm_dma_request_chan()

Hello,

Am Fri, Jan 24, 2025 at 09:52:20AM +0100 schrieb Bence Csókás:
> Expand the arsenal of devm functions for DMA
> devices, this time for requesting channels.
> 
> Signed-off-by: Bence Csókás <csokas.bence@...lan.hu>
> ---
>  drivers/dma/dmaengine.c   | 30 ++++++++++++++++++++++++++++++
>  include/linux/dmaengine.h |  7 +++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index c1357d7f3dc6..02c29d26ac85 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -926,6 +926,36 @@ void dma_release_channel(struct dma_chan *chan)
>  }
>  EXPORT_SYMBOL_GPL(dma_release_channel);
>  
> +static void dmaenginem_release_channel(void *chan)
> +{
> +	dma_release_channel(chan);
> +}
> +
> +/**
> + * devm_dma_request_chan - try to allocate an exclusive slave channel
> + * @dev:	pointer to client device structure
> + * @name:	slave channel name
> + *
> + * Returns pointer to appropriate DMA channel on success or an error pointer.
> + *
> + * The operation is managed and will be undone on driver detach.
> + */
> +
> +struct dma_chan *devm_dma_request_chan(struct device *dev, const char *name)
> +{
> +	struct dma_chan *chan = dma_request_chan(dev, name);
> +	int ret = 0;
> +
> +	if (!IS_ERR(chan))
> +		ret = devm_add_action_or_reset(dev, dmaenginem_release_channel, chan);

Why not using dma_release_channel() directly here?  What's the point
of introducing dmaenginem_release_channel() further above?

Greets
Alex

> +
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	return chan;
> +}
> +EXPORT_SYMBOL_GPL(devm_dma_request_chan);
> +
>  /**
>   * dmaengine_get - register interest in dma_channels
>   */
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 346251bf1026..ffb54b52ef0c 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -1528,6 +1528,7 @@ struct dma_chan *__dma_request_channel(const dma_cap_mask_t *mask,
>  
>  struct dma_chan *dma_request_chan(struct device *dev, const char *name);
>  struct dma_chan *dma_request_chan_by_mask(const dma_cap_mask_t *mask);
> +struct dma_chan *devm_dma_request_chan(struct device *dev, const char *name);
>  
>  void dma_release_channel(struct dma_chan *chan);
>  int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps);
> @@ -1564,6 +1565,12 @@ static inline struct dma_chan *dma_request_chan_by_mask(
>  {
>  	return ERR_PTR(-ENODEV);
>  }
> +
> +static inline struct dma_chan *devm_dma_request_chan(struct device *dev, const char *name)
> +{
> +	return ERR_PTR(-ENODEV);
> +}
> +
>  static inline void dma_release_channel(struct dma_chan *chan)
>  {
>  }
> -- 
> 2.48.1
> 
> 
>