Re: [RFC v02 00/15] dmaengine: New 'universal' API for requesting channel

Arnd Bergmann
2015-11-30T14:18:39Z

On Monday 30 November 2015 15:45:30 Peter Ujfalusi wrote:
> Changes since RFC v01:
>- dma_request_chan(); lost the mask parameter
>- The new API does not rely on RESOURCE_DMA, instead the dma_filter_map table
> will be used to provide the needed information to the filter function in
> legacy mode
>- Extended the example patches to convert most of daVinci to use the new API to
> request the DMA channels.

Very nice overall. Just a few minor comments.

> static struct dma_filter_map da830_edma_map[] = {
> DMA_FILTER_ENTRY("davinci-mcasp.0", "rx", EDMA_CTLR_CHAN(0, 0)),
> DMA_FILTER_ENTRY("davinci-mcasp.0", "tx", EDMA_CTLR_CHAN(0, 1)),
> DMA_FILTER_ENTRY("davinci-mcasp.1", "rx", EDMA_CTLR_CHAN(0, 2)),
> DMA_FILTER_ENTRY("davinci-mcasp.1", "tx", EDMA_CTLR_CHAN(0, 3)),
> DMA_FILTER_ENTRY("davinci-mcasp.2", "rx", EDMA_CTLR_CHAN(0, 4)),
> DMA_FILTER_ENTRY("davinci-mcasp.2", "tx", EDMA_CTLR_CHAN(0, 5)),
> DMA_FILTER_ENTRY("spi_davinci.0", "rx", EDMA_CTLR_CHAN(0, 14)),
> DMA_FILTER_ENTRY("spi_davinci.0", "tx", EDMA_CTLR_CHAN(0, 15)),
> DMA_FILTER_ENTRY("da830-mmc.0", "rx", EDMA_CTLR_CHAN(0, 16)),
> DMA_FILTER_ENTRY("da830-mmc.0", "tx", EDMA_CTLR_CHAN(0, 17)),
> DMA_FILTER_ENTRY("spi_davinci.1", "rx", EDMA_CTLR_CHAN(0, 18)),
> DMA_FILTER_ENTRY("spi_davinci.1", "tx", EDMA_CTLR_CHAN(0, 19)),
> };

I wonder if we should mandate that the lookup table is 'const'.

We could also drop the DMA_FILTER_ENTRY() macro above, and open-code the
table like

static struct dma_filter_map da830_edma_map[] = {
{ "davinci-mcasp.0", "rx", EDMA_CTLR_CHAN(0, 0)},
{ "davinci-mcasp.0", "tx", EDMA_CTLR_CHAN(0, 1)},
{ "davinci-mcasp.1", "rx", EDMA_CTLR_CHAN(0, 2)},
...
};

which is a little more compact and more obvious, but loses the
named initializers.

Arnd