RFC: changing DMA slave configuration API

[Barry Song]

2012/6/10 Russell King - ARM Linux <linux at 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;

it seems that might mean an union in your dma_slave_cfg, but not
co-exitense of both?

struct dma_slave_cfg {
+       union {
              struct dma_dev_cfg dev_src;
              struct dma_dev_cfg dev_dst;
       }
       bool device_fc;
};

>
> 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);
>
Thanks
barry