Re: [PATCH 08/18] dma-mapping: add a new dma_alloc_noncoherent API

[Robin Murphy]

On 2020-09-15 16:51, Christoph Hellwig wrote:
[...]
> +These APIs allow to allocate pages in the kernel direct mapping that are
> +guaranteed to be DMA addressable.  This means that unlike dma_alloc_coherent,
> +virt_to_page can be called on the resulting address, and the resulting

Nit: if we explicitly describe this as if it's a guarantee that can be 
relied upon...

> +struct page can be used for everything a struct page is suitable for.

[...]
> +This routine allocates a region of <size> bytes of consistent memory.  It
> +returns a pointer to the allocated region (in the processor's virtual address
> +space) or NULL if the allocation failed.  The returned memory may or may not
> +be in the kernels direct mapping.  Drivers must not call virt_to_page on
> +the returned memory region.

...then forbid this document's target audience from relying on it, 
something seems off. At the very least it's unhelpfully unclear :/

Given patch #17, I suspect that the first paragraph is the one that's no 
longer true.

Robin.