Re: can device drivers return non-ram via vm_ops->nopage?

[Russell King <rmk+lkml@arm.linux.org.uk>]

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);
#else
#warning What do we have to do here??
#endif

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   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core