# Re: \[RFC PATCH v3 4/6\] swiotlb: Add restricted DMA alloc/free support.

- From: Florian Fainelli \<f.fainelli@gmail.com\>
- Date: 2021-01-13 00:43:09 
- List: linux-devicetree
- Page: https://ratatoskr.run/linux-devicetree/2021/01/6232629
- Thread: https://ratatoskr.run/linux-devicetree/2021/01/6224988/t.md

```text
On 1/5/21 7:41 PM, Claire Chang wrote:
> Add the functions, swiotlb_alloc and swiotlb_free to support the
> memory allocation from restricted DMA pool.
> 
> Signed-off-by: Claire Chang <redacted>
> ---

[snip]

> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 30ccbc08e229..126e9b3354d6 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -137,6 +137,11 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>  	void *ret;
>  	int err;
>  
> +#ifdef CONFIG_SWIOTLB
> +	if (unlikely(dev->dma_io_tlb_mem))
> +		return swiotlb_alloc(dev, size, dma_handle, attrs);
> +#endif

While this is potentially a hot path, I am not sure of the unkikely is
warranted, maybe best left as a plain conditional.
-- 
Florian
```