Re: [patch 1/2] powerpc: rmb fix

[Nick Piggin <npiggin@suse.de>]

On Wed, Aug 22, 2007 at 05:33:16AM +0200, Segher Boessenkool wrote:
> >>The I/O accessor functions enforce the necessary ordering
> >>already I believe.
> >
> >Hmm, I never followed those discussions last year about IO ordering, 
> >and
> >I can't see where (if) it was documented anywhere :(
> 
> The comments in system.h weren't updated with the last fix, I think.
> 
> >It appears that legacy code is handled by defining the old IO 
> >accessors to
> >be completely ordered, and introducing new __raw_ variants that are not
> >(OTOH, it seems like other architectures are implementing __raw prefix 
> >as
> >inorder unless there is a _relaxed postfix).
> 
> __raw_XX() is for platform code only, which can do the needed
> barriers without having to use the heavy hammer like everything
> else unfortunately does.


npiggin@nick:~/usr/src/linux-2.6/drivers> egrep '__raw_(write|read)' -r * | wc -l
685

 
> >Drivers are definitely using these __raw_ accessors, and from a quick
> >look, they do appear to be hoping that *mb() is going to order access 
> >for
> >them.
> 
> Which drivers?

There are maybe a dozen that use the raw accessors, and use non-smp_
memory barriers. I just looked at drivers/video/tgafb.c, which
indeed appears to intermix them.