Re: [PATCH v7 2/2] ARM hibernation / suspend-to-disk

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Mon, Mar 10, 2014 at 11:32:17AM -0700, Sebastian Capella wrote:
> I've moved to this second implementation.  I don't think I understand
> the ramifications enough to add the virt_to_pfn call for arm.

Let's look at the implementations...

#define __pa(x)                 __virt_to_phys((unsigned long)(x))
static inline phys_addr_t __virt_to_phys(unsigned long x)
{
        return (phys_addr_t)x - PAGE_OFFSET + PHYS_OFFSET;
}

So, __pa() returns a phys_addr_t (which may be either 32-bit or 64-bit).

#define virt_to_pfn(kaddr)  (__pa(kaddr) >> PAGE_SHIFT)

And that will do an appropriate shift to convert the phys_addr_t to a PFN,
which will be fine to assign to an unsigned long variable.

#define __phys_to_pfn(paddr)    ((unsigned long)((paddr) >> PAGE_SHIFT))

This does the same thing, but has an explicit cast.

So, the only difference between the two suggestions is that additional
cast, which has no effect here.

> I've changed one thing.  __nosave_end is pointing at the first byte
> not included in the nosave region.  I subtracted one from it so that
> we make sure we're referring to the last pfn, and left the pfn
> comparison as you'd suggested.

Yes, that should be safer.

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