RFC: changing DMA slave configuration API

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

Dan, Vinod,

There's a change I would like to do to the DMA slave configuration.
It's currently a pain to have the source and destination parameters in
the dma_slave_config structure as separate elements; it means when you
want to extract them, you end up with code in DMA engine drivers like:

+	if (dir == DMA_DEV_TO_MEM) {
+		dev_addr = c->src_addr;
+		dev_width = c->src_addr_width;
+		burst = c->src_maxburst;
+	} else if (dir == DMA_MEM_TO_DEV) {
+		dev_addr = c->dst_addr;
+		dev_width = c->dst_addr_width;
+		burst = c->dst_maxburst;
+	}

If we redefine the structure as below, this all becomes more simple:

+	if (dir == DMA_DEV_TO_MEM)
+		cfg = &c->dev_src;
+	else if (dir == DMA_MEM_TO_DEV)
+		cfg = &c->dev_dst;

and then we can access the data through cfg->{element} rather than having
to cache each individual elements value in a local variable.

Thoughts?

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 56377df..e6519f7 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -367,6 +367,18 @@ struct dma_slave_config {
 	bool device_fc;
 };
 
+struct dma_dev_cfg {
+	dma_addr_t addr;
+	enum dma_slave_buswidth width;
+	u32 maxburst;
+};
+
+struct dma_slave_cfg {
+	struct dma_dev_cfg dev_src;
+	struct dma_dev_cfg dev_dst;
+	bool device_fc;
+};
+
 static inline const char *dma_chan_name(struct dma_chan *chan)
 {
 	return dev_name(&chan->dev->device);