> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> + if (swiotlb_free(dev, page, size))
> + return;
> +#endif
Please avoid the ifdefs by either stubbing out the function to be a no-op
or by using IS_ENABLED.
> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> + page = swiotlb_alloc(dev, size);
> +
The restricted DMA pool is preferred if available.
The restricted DMA pools provide a basic level of protection against the
DMA overwriting buffer contents at unexpected times. However, to protect
against general data leakage and system memory corruption, the system
needs to provide a way to lock
