Re: [PATCH 13/17] RISC-V: Add include subdirectory

[Benjamin Herrenschmidt]

On Fri, 2017-06-23 at 19:01 -0700, Palmer Dabbelt wrote:
> > > +#define mmiowb()ÂÂÂÂÂÂ __asm__ __volatile__ ("fence io,io" : : : "memory");

I forgot if we already mentioned that but mmiowb is primarily intended
to order MMIO stores vs. a subsequent spin_unlock.

I'm not sure an IO only fence is sufficient here.

Note that I've never trusted drivers to get that right, it's a rather
bad abstraction to begin with, so on powerpc, instead, I just set a
per-cpu flag on every non-relaxed MMIO write and test it in spin_unlock
in order to "beef up" the barrier in there if necessary.

Cheers,
Ben.