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SubjectRe: can device drivers return non-ram via vm_ops->nopage?
On Sun, Mar 21, 2004 at 07:10:53PM -0500, Jeff Garzik wrote:
> For the first kind, please read fb_mmap in drivers/video/fbmem.c. Look
> at the _horror_ of ifdefs in exporting the framebuffer. And that horror
> is what's often needed when letting userspace mmap(2) PCI memory IO regions.

Most of this:

#if defined(__mc68000__)
#elif defined(__mips__)
pgprot_val(vma->vm_page_prot) &= ~_CACHE_MASK;
pgprot_val(vma->vm_page_prot) |= _CACHE_UNCACHED;
#elif defined(__sh__)
pgprot_val(vma->vm_page_prot) &= ~_PAGE_CACHABLE;
#elif defined(__hppa__)
pgprot_val(vma->vm_page_prot) |= _PAGE_NO_CACHE;
#elif defined(__ia64__) || defined(__arm__)
vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
#warning What do we have to do here??

exists because architectures haven't defined their private
pgprot_writecombine() implementations, preferring instead to add
to the preprocessor junk instead.

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