Re: [PATCH 1/5] Make __pa() uses CPHYSADDR() if really needed

[Franck Bui-Huu <vagabon.xyz@gmail.com>]

Atsushi Nemoto wrote:
> On Wed, 11 Oct 2006 18:01:43 +0200, Franck Bui-Huu <vagabon.xyz@gmail.com> wrote:
>>> __pa() is used in many place indirectly via virt_to_page().
>> what about make virt_to_page() use virt_to_phys() instead ?
> 
> No objection for virt_to_phys(), but I found other __pa() usages in
> kernel.
> 
> drivers/char/mem.c:       && addr >= __pa(high_memory);
> drivers/char/mem.c:     return addr >= __pa(high_memory);
> drivers/char/mem.c:     if (addr + count > __pa(high_memory))
> drivers/char/mem.c:     pfn = __pa((u64)vma->vm_pgoff << PAGE_SHIFT) >> PAGE_SHIFT;
> 
> So __pa() should handle >512MB address unless we change all __pa() usages.

weird, I really thought that __pa() shouldn't be used by drivers...
Let see what people on lkml think about this usage, you'll be CC'ed
if you want to.

> 
> How about something like this ?
> 
> #if defined(CONFIG_64BITS) && !defined(CONFIG_BUILD_ELF64)
> #define __pa(x)			((unsigned long)(x) - ((unsigned long)(x) >= CKSEG0 ? CKSEG0 : PAGE_OFFSET))
> #else
> #define __pa(x)			((unsigned long)(x) - PAGE_OFFSET)
> #endif
> 

It would be safer indeed, specially because __pa() definition is not
really well defined and seems to be confusing for most people.

> In any case, I think virt_to_page() should use simpler virt_to_phys()
> for better performance.

I agree.

		Franck