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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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