linux-kernel - Re: [PATCHv9] dmaengine: Add support for BCM2835

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Date:	Thu, 02 Jan 2014 19:03:34 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Florian Meier <florian.meier@...lo.de>,
	Stephen Warren <swarren@...dotorg.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	devicetree <devicetree@...r.kernel.org>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mark Brown <broonie@...nel.org>,
	linux-rpi-kernel <linux-rpi-kernel@...ts.infradead.org>,
	dmaengine <dmaengine@...r.kernel.org>,
	Stephen Warren <swarren@...dia.com>
Subject: Re: [PATCHv9] dmaengine: Add support for BCM2835

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
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