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

On Wed, Aug 22, 2007 at 05:33:16AM +0200, Segher Boessenkool wrote:

quoted

quoted

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.

quoted

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

 

quoted

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.