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.