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SubjectRe: can device drivers return non-ram via vm_ops->nopage?
On Sun, Mar 21, 2004 at 03:11:58PM -0800, Linus Torvalds wrote:
> On Sun, 21 Mar 2004, Russell King wrote:
> > Remember that we're fond of telling driver writers to use scatter gather
> > lists rather than grabbing one large contiguous memory chunk... So
> > they did exactly as we told them. Using pci_alloc_consistent and/or
> > dma_alloc_coherent and built their own scatter lists.
> I do think that we should introduce a "map_dma_coherent()" thing, which
> basically takes a list of pages that have been allocated by
> dma_alloc_coherent(), and remaps them into user space. How hard can that
> be?
> In fact, on a lot of architectures (well, at least x86, and likely
> anything else that doesn't use any IOTLB and just allocates a chunk of
> physical memory), I think the "map_dma_coherent()" thing should basically
> just become a "remap_page_range()". Ie something like
> #define map_dma_coherent(vma, vaddr, len) \
> remap_page_range(vma, vma->vm_start, __pa(vaddr), len, vma->vm_page_prot)
> for the simple case.

Ok, splitting hairs, for the coherent contiguous case, what about:

int dma_coherent_map(struct vm_area_struct *vma, void *cpu_addr,
dma_addr_t dma_addr, size_t size);

and x86 would be:

#define dma_coherent_map(vma,cpu_addr,dma_addr,size) \
remap_page_range(vma, vma->vm_start, __pa(cpu_addr), \
size, vma->vm_page_prot)

This then leaves the PCI BAR case and the DMA coherent SG buffer case,
though neither of those fall within my personal problem space at present.

Russell King
Linux kernel 2.6 ARM Linux -
maintainer of: 2.6 PCMCIA -
2.6 Serial core
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