linux-kernel - Re: [RFC/PATCH] dma: of: Make of_dma_simple_xlate match on DMA device and channel ID

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Message-ID: <51938FFD.2020300@metafoo.de>
Date:	Wed, 15 May 2013 15:39:09 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:	linux-kernel@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <djbw@...com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Peter Ujfalusi <peter.ujfalusi@...com>
Subject: Re: [RFC/PATCH] dma: of: Make of_dma_simple_xlate match on DMA device
 and channel ID

On 05/15/2013 03:27 PM, Laurent Pinchart wrote:
> When translating a DT DMA channel specifier, the most common use case is
> to match the DMA channel based on the channel DMA engine and channel ID.
> Modify the of_dma_simple_xlate() function to do so, simplifying the API
> for DMA engine drivers.
> 
> There is no need to check the DMA cells count in the filter function as
> the check is already performed by the caller in of_dma_get_controller().
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

Hi,

I've submitted a very similar patch some time ago, see
https://lkml.org/lkml/2013/3/25/250

- Lars

> ---
>  drivers/dma/of-dma.c   | 39 +++++++++++++++++++++++++++++++--------
>  drivers/dma/omap-dma.c |  8 +-------
>  include/linux/of_dma.h |  5 -----
>  3 files changed, 32 insertions(+), 20 deletions(-)
> 
> I've implemented this function while working on a DMA engine driver, and
> realized that it wasn't specific to my driver at all. As I'm new to the DMA
> engine API, I'd appreciate feedback on whether this change makes sense, or if
> I should instead keep the existing of_dma_simple_xlate() function and create a
> separate simple xlate helper.
> 
> diff --git a/drivers/dma/of-dma.c b/drivers/dma/of-dma.c
> index 7aa0864..702a45d 100644
> --- a/drivers/dma/of-dma.c
> +++ b/drivers/dma/of-dma.c
> @@ -202,6 +202,27 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
>  	return NULL;
>  }
>  
> +struct of_dma_filter_args {
> +	struct dma_device *device;
> +	unsigned int chan_id;
> +};
> +
> +/**
> + * of_dma_simple_xlate_filter - Channel filter function for of_dma_simple_xlate
> + * @dma_chan:	pointer to candidate DMA channel
> + * @param:	pointer to filter parameter
> + *
> + * Filter out candidate DMA channels that don't match the channel ID or DMA
> + * engine device passed as arguments.
> + */
> +static bool of_dma_simple_xlate_filter(struct dma_chan *chan, void *param)
> +{
> +	struct of_dma_filter_args *fargs = param;
> +
> +	return (chan->device == fargs->device) &&
> +	       (chan->chan_id == fargs->chan_id);
> +}
> +
>  /**
>   * of_dma_simple_xlate - Simple DMA engine translation function
>   * @dma_spec:	pointer to DMA specifier as found in the device tree
> @@ -216,16 +237,18 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
>  struct dma_chan *of_dma_simple_xlate(struct of_phandle_args *dma_spec,
>  						struct of_dma *ofdma)
>  {
> -	int count = dma_spec->args_count;
> -	struct of_dma_filter_info *info = ofdma->of_dma_data;
> +	struct dma_device *dev = ofdma->of_dma_data;
> +	struct of_dma_filter_args fargs;
> +	dma_cap_mask_t cap;
>  
> -	if (!info || !info->filter_fn)
> -		return NULL;
> +	/* There's no need to specify matching caps as we're going to match a
> +	 * specific DMA channel anyway.
> +	 */
> +	dma_cap_zero(cap);
>  
> -	if (count != 1)
> -		return NULL;
> +	fargs.device = dev;
> +	fargs.chan_id = dma_spec->args[0];
>  
> -	return dma_request_channel(info->dma_cap, info->filter_fn,
> -			&dma_spec->args[0]);
> +	return dma_request_channel(cap, of_dma_simple_xlate_filter, &fargs);
>  }
>  EXPORT_SYMBOL_GPL(of_dma_simple_xlate);
> diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c
> index ec3fc4f..7e7ff06 100644
> --- a/drivers/dma/omap-dma.c
> +++ b/drivers/dma/omap-dma.c
> @@ -69,10 +69,6 @@ static const unsigned es_bytes[] = {
>  	[OMAP_DMA_DATA_TYPE_S32] = 4,
>  };
>  
> -static struct of_dma_filter_info omap_dma_info = {
> -	.filter_fn = omap_dma_filter_fn,
> -};
> -
>  static inline struct omap_dmadev *to_omap_dma_dev(struct dma_device *d)
>  {
>  	return container_of(d, struct omap_dmadev, ddev);
> @@ -641,11 +637,9 @@ static int omap_dma_probe(struct platform_device *pdev)
>  	platform_set_drvdata(pdev, od);
>  
>  	if (pdev->dev.of_node) {
> -		omap_dma_info.dma_cap = od->ddev.cap_mask;
> -
>  		/* Device-tree DMA controller registration */
>  		rc = of_dma_controller_register(pdev->dev.of_node,
> -				of_dma_simple_xlate, &omap_dma_info);
> +				of_dma_simple_xlate, &od->ddev);
>  		if (rc) {
>  			pr_warn("OMAP-DMA: failed to register DMA controller\n");
>  			dma_async_device_unregister(&od->ddev);
> diff --git a/include/linux/of_dma.h b/include/linux/of_dma.h
> index 364dda7..3c0d9ac 100644
> --- a/include/linux/of_dma.h
> +++ b/include/linux/of_dma.h
> @@ -27,11 +27,6 @@ struct of_dma {
>  	void			*of_dma_data;
>  };
>  
> -struct of_dma_filter_info {
> -	dma_cap_mask_t	dma_cap;
> -	dma_filter_fn	filter_fn;
> -};
> -
>  #ifdef CONFIG_OF
>  extern int of_dma_controller_register(struct device_node *np,
>  		struct dma_chan *(*of_dma_xlate)

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