On Fri, Sep 25, 2020 at 12:15:37PM +0100, Robin Murphy wrote: > 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. Yes. dma_alloc_pages is the replacement for allocations that need the direct mapping. I'll send a patch to document dma_alloc_pages and fixes this up
