Re: [PATCH 7/8] docs: dma-api: update streaming DMA API physical address constraints

[Bagas Sanjaya]

On Tue, Jun 24, 2025 at 03:39:22PM +0200, Petr Tesarik wrote:
> diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
> index cd432996949c..65132ec88104 100644
> --- a/Documentation/core-api/dma-api.rst
> +++ b/Documentation/core-api/dma-api.rst
> @@ -210,18 +210,12 @@ DMA_BIDIRECTIONAL	direction isn't known
>  	this API should be obtained from sources which guarantee it to be
>  	physically contiguous (like kmalloc).
>  
> -	Further, the DMA address of the memory must be within the dma_mask of
> -	the device.  To ensure that the memory allocated by kmalloc is within
> -	the dma_mask, the driver may specify various platform-dependent flags
> -	to restrict the DMA address range of the allocation (e.g., on x86,
> -	GFP_DMA guarantees to be within the first 16MB of available DMA
> -	addresses, as required by ISA devices).
> -
> -	Note also that the above constraints on physical contiguity and
> -	dma_mask may not apply if the platform has an IOMMU (a device which
> -	maps an I/O DMA address to a physical memory address).  However, to be
> -	portable, device driver writers may *not* assume that such an IOMMU
> -	exists.
> +	Mapping may also fail if the memory is not within the DMA mask of the
> +	device.  However, this constraint does not apply if the platform has
> +	an IOMMU (a device which maps an I/O DMA address to a physical memory
> +	address), or the kernel is configured with SWIOTLB (bounce buffers).
> +	It is reasonable to assume that at least one of these mechanisms
> +	allows streaming DMA to any physical address.
>  
>  .. warning::
>  

LGTM, thanks!

Reviewed-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx>

-- 
An old man doll... just what I always wanted! - Clara

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