Re: [PATCH V2 2/2] dmaengine: tegra-adma: Add support for Tegra210 ADMA

[Arnd Bergmann <arnd@arndb.de>]

On Monday 05 October 2015 13:10:07 Jon Hunter wrote:
> Add support for the Tegra210 Audio DMA controller that is used for
> transferring data between system memory and the Audio sub-system.
> The driver only supports cyclic transfers because this is being solely
> used for audio.
> 
> This driver is based upon the work by Dara Ramesh <dramesh@nvidia.com>.
> 
> Signed-off-by: Jon Hunter <jonathanh@nvidia.com>

This version looks much better!

Just one small comment:

> +	slave_req = dma_spec->args[0];
> +	slave_dir = dma_spec->args[1];
> +
> +	if (slave_req == 0)
> +		return NULL;
> +
> +	switch (slave_dir) {
> +	case ADMA_AHUB_TO_MEM:
> +		if (slave_req > tdma->rx_requests)
> +			return NULL;
> +
> +		if (tdma->rx_requests_reserved & BIT(slave_req))
> +			return NULL;
> +
> +		tdma->rx_requests_reserved |= BIT(slave_req);
> +		break;

The rx_requests_reserved logic looks racy, if you have more than
one concurrent request or release. Better use atomic_test_and_set()
here and turn the variable into an atomic_t.

	Arbd