[PATCH v3 4/4] dmaengine: add union chan_dev for dma_chan::dev for clarity

[Andy Shevchenko]

On Fri, Sep 04, 2026 at 05:49:46PM -0400, Frank.Li at oss.nxp.com wrote:

> The current dma_chan structure contains both "device" and "dev". So
> 
> chan->device->dev refers to the DMA engine device.
> chan->dev->device refers to the per-channel device instance.
> 
> Their similar naming makes the distinction unclear and increases reader
> confusion.
> 
> Add union dma_chan::chan_dev to make its purpose explicit and clearly
> identify it as the per-channel device. After all user switch to chan_dev,
> union and dma_chan::dev will be removed.
> 
> Update the kernel-doc accordingly. Besides its sysfs usage, the per-channel
> device is also used by some DMA engine drivers for IOMMU mapping and
> therefore deserves a more accurate description.
> 
> No functional change intended.

I was almost ready to give a tag for the entire series, but found a minor
issue here...

...

> +++ b/include/linux/dmaengine.h
> struct dma_router {

>   * @lock: protect between config and prepare transfer when driver have not
>   *	  implemented callback device_prep_config_sg().
>   * @chan_id: channel ID for sysfs
> - * @dev: class device for sysfs
> + * @chan_dev: class channel device for sysfs, some device use it for per-channel
> + *            iommu mapping.

IOMMU

>   * @name: backlink name for sysfs
>   * @dbg_client_name: slave name for debugfs in format:
>   *	dev_name(requester's dev):channel name, for example: "2b00000.mcasp:tx"

> struct dma_chan {

>  
>  	/* sysfs */
>  	int chan_id;
> -	struct dma_chan_dev *dev;
> +	union {
> +		struct dma_chan_dev *chan_dev;
> +		/*
> +		 * please use chan_dev, dev will be removed after all user
> +		   switch to chan_dev
> +		*/

Something went wrong with this comment style. It also need to respect English
grammar and punctuation as we do for multi-line comments.

> +		struct dma_chan_dev *dev;
> +	};
>  	const char *name;
>  #ifdef CONFIG_DEBUG_FS
>  	char *dbg_client_name;

-- 
With Best Regards,
Andy Shevchenko