Re: [PATCH] dmaengine: Add hisilicon k3 DMA engine driver

On Tue, Jun 18, 2013 at 04:09:14PM +0200, Arnd Bergmann wrote:

On Tuesday 18 June 2013, zhangfei gao wrote:

quoted

On Tue, Jun 18, 2013 at 4:58 AM, Arnd Bergmann [off-list ref] wrote:

quoted

quoted

+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.

for SW muxes this may work well IMO

--
~Vinod