Re: [PATCHv9] dmaengine: Add support for BCM2835

Arnd Bergmann
2014-01-02T18:03:49Z

On Thursday 02 January 2014 18:49:23 Florian Meier wrote:
> Add support for DMA controller of BCM2835 as used in the Raspberry Pi.
> Currently it only supports cyclic DMA.

Looks very nice. Just a few details I noticed:

> +#if defined(CONFIG_OF)
> +static const struct of_device_id bcm2835_dma_of_match[] = {
> + { .compatible = "brcm,bcm2835-dma", },
> + {},
> +};
> +MODULE_DEVICE_TABLE(of, bcm2835_dma_of_match);
> +#endif

I doubt we are going to see non-DT versions of this driver, so the #ifdef
can just get removed here.

> +static struct dma_chan *bcm2835_dma_xlate(struct of_phandle_args *spec,
> + struct of_dma *ofdma)
> +{
> + struct bcm2835_dmadev *d = ofdma->of_dma_data;
> + struct dma_chan *chan, *candidate;
> +
> +retry:
> + candidate = NULL;
> +
> + /*
> + * Walk the list of channels registered with the current instance and
> + * find one that is currently unused.
> + */
> + list_for_each_entry(chan, &d->ddev.channels, device_node)
> + if (chan->client_count == 0) {
> + candidate = chan;
> + break;
> + }
> +
> + if (!candidate)
> + return NULL;
> +
> + /*
> + * dma_get_slave_channel will return NULL if we lost a race between
> + * the lookup and the reservation.
> + */
> + chan = dma_get_slave_channel(candidate);
> +
> + if (!chan)
> + goto retry;
> +
> + /* Set DREQ from param */
> + to_bcm2835_dma_chan(chan)->dreq = spec->args[0];
> +
> + return chan;
> +}

This can now be simplified using the dma_get_any_slave_channel() interface
taht Stephen Warren introduced.

> +
> + if (!pdev->dev.dma_mask)
> + pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask;
> +
> + rc = dma_set_mask(&pdev->dev, DMA_BIT_MASK(32));
> + if (rc)
> + return rc;
> + dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32));

dma_set_mask_and_coherent()

> + if (pdev->dev.of_node) {
> + /* Device-tree DMA controller registration */
> + rc = of_dma_controller_register(pdev->dev.of_node,
> + bcm2835_dma_xlate, od);
> + if (rc) {
> + dev_err(&pdev->dev, "Failed to register DMA controller\n");
> + goto err_no_dma;
> + }
> + }

If pdev->dev.of_node isn't set, you didn't get here, so the if() can be removed.

Arnd