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

Peter Ujfalusi
2015-12-01T10:12:47Z

On 11/30/2015 04:18 PM, Arnd Bergmann wrote:
> 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'.

I had been wondering the same, I'll make it const for the next round.

> 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.

We would need:
{ "da830-mmc.0", "rx", (void*)EDMA_CTLR_CHAN(0, 16) },
{ "da830-mmc.0", "tx", (void*)EDMA_CTLR_CHAN(0, 17) },

as we need to cast the param.
It is still compact, but having to add the (void*) casting makes it a bit ugly.

--
Péter
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