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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