On Sun, 2013-11-17 at 16:39 +0100, Florian Meier wrote:
> Add support for DMA controller of BCM2835 as used in the Raspberry Pi.
> Currently it only supports cyclic DMA.
[]
> diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
[]
> +static int bcm2835_dma_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
> + unsigned long arg)
> +{
> + struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
> + int ret;
> +
> + switch (cmd) {
> + case DMA_SLAVE_CONFIG:
> + return bcm2835_dma_slave_config(c,
> + (struct dma_slave_config *)arg);
> +
> + case DMA_TERMINATE_ALL:
> + bcm2835_dma_terminate_all(c);
> + break;
> +
> + default:
> + ret = -ENXIO;
> + break;
> + }
> +
> + return ret;
> +}
case DMA_TERMINATE_ALL returns an uninitialized ret;
[]
> +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);
Can that race happen consistently?
Does this avoid being a tight loop?
> + if (chan) {
> + struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
> +
> + /* Set DREQ from param */
> + c->dreq = spec->args[0];
> +
> + return chan;
> + }
> +
> + goto retry;
> +}
Also, I think this would be better as:
if (!chan)
goto retry;
to_bcm2835_dma_chan(chan)->dreq = spec->args[0];
return chan;
}
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