Subject: [RFC/PATCH] dma: of: Make of_dma_simple_xlate match on DMA device and channel ID

From: [email-masked] (Laurent Pinchart)
Date: Wed, 15 May 2013 15:55:45 +0200

Hi Lars-Peter,

(CC'ing LAKML, I had forgotten to do so when I sent the patch)

On Wednesday 15 May 2013 15:39:09 Lars-Peter Clausen wrote:
> 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 <[email-masked]>
> 
> Hi,
> 
> I've submitted a very similar patch some time ago, see
> https://lkml.org/lkml/2013/3/25/250

Thanks. So my patch makes at least some sense :-)

I had the impression that this is what omap-dma needs as well, hence the 
modification to the existing xlate function. I'm fine with a separate function 
as well if the current code covers different use cases.

> > ---
> > 
> >  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)
-- 
Regards,

Laurent Pinchart