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


  • To: Claire Chang <tientzu@xxxxxxxxxxxx>, robh+dt@xxxxxxxxxx, mpe@xxxxxxxxxxxxxx, benh@xxxxxxxxxxxxxxxxxxx, paulus@xxxxxxxxx, joro@xxxxxxxxxx, will@xxxxxxxxxx, frowand.list@xxxxxxxxx, konrad.wilk@xxxxxxxxxx, boris.ostrovsky@xxxxxxxxxx, jgross@xxxxxxxx, sstabellini@xxxxxxxxxx, hch@xxxxxx, m.szyprowski@xxxxxxxxxxx, robin.murphy@xxxxxxx
  • From: Florian Fainelli <f.fainelli@xxxxxxxxx>
  • Date: Tue, 12 Jan 2021 15:41:46 -0800
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  • Delivery-date: Tue, 12 Jan 2021 23:41:55 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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 <tientzu@xxxxxxxxxxxx>
> ---

[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



 


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