Re: [PATCH] UIO: only call pgprot_noncached if defined

[Hans J. Koch]

On Wed, Nov 05, 2008 at 12:33:37PM -0500, Mike Frysinger wrote:
> On Wed, Nov 5, 2008 at 11:33, Greg KH wrote:
> > On Wed, Nov 05, 2008 at 12:36:11PM +0100, Hans J. Koch wrote:
> >> There seem to be archs that cannot easily implement a sensible
> >> pgprot_noncached() function, so we should merge this patch. UIO doesn't
> >> compile on these archs right now.
> >
> > No, we should fix those arches to have that function at least NULLed
> > out.  Isn't there only one, Blackfin?  Putting #ifdefs in .c files is
> > not something we really want to do if at all possible.
> 
> that was my question.  this function isnt documented.  if the hardware
> doesnt support it, is the right thing really for the arch to lie to
> drivers and not actually give back cached settings even though it
> asked for non-cached ?

Well, if there's no possibility to map device memory in a non-cached
way, it's very likely you don't want to use UIO at all. If there's a few
seconds between a write and the value actually appearing in the hardware
register, you will certainly don't see the results you expect.

If Blackfin can't mmap non-cached memory, we should make UIO depend on
!BLACKFIN.

Hans
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/