[PATCH] dmaengine: Add hisilicon k3 DMA engine driver

[Arnd Bergmann]

On Tuesday 18 June 2013, zhangfei gao wrote:
> On Tue, Jun 18, 2013 at 4:58 AM, Arnd Bergmann <arnd at arndb.de> wrote:
> >
> >> +static struct of_dma_filter_info k3_dma_filter;
> >> +static bool k3_dma_filter_fn(struct dma_chan *chan, void *param)
> >> +{
> >> +     return  (*(int *)param == chan->chan_id);
> >> +}
> >
> > This filter function works only as long as there is no more than
> > one DMA engine in the system, which is something that needs to
> > be documented better. Unfortunately, providing a filter
> > function to be called by .xlate is currently the only way that
> > the dma-engine API supports, but we should really get over that.
> >
> > Vinod: I think we need to add a way for a dmaengine driver to
> > just return one of its channels to the xlate function. The
> > current method is getting very silly, and it adds run-time and
> > code complexity without any need.
> >
> > How about something like
> >
> > int dma_get_slave_channel(struct dma_chan *chan)
> > {
> >         /* lock against __dma_request_channel */
> >         mutex_lock(&dma_list_mutex);
> >
> >         if (chan->client_count == 0)
> >                 ret = dma_chan_get(chan);
> >         else
> >                 ret = -EBUSY;
> >
> >         mutex_unlock(&dma_list_mutex);
> >
> >         return ret;
> > }
> > EXPORT_SYMBOL_GPL(dma_get_slave_channel);
> 
> Want to double check here.
> Device need specific channel via request line, the requirement still
> can be met, right?

The driver can have a simple array of pointers that is indexed by
the request number, so you end up with something like

struct dma_chan *of_dma_simple_xlate(struct of_phandle_args *dma_spec,
                                                struct of_dma *ofdma)
{
        struct k3_dma_dev *dev = ofdma->of_dma_data;
	unsigned int vchan = dma_spec->args[0];

	if (vchan > dev->nr_channels)
		return NULL;

        return dma_get_slave_channel(dev->vchan[vchan]);
}

With no need to have a filter function.

	Arnd