Re: [PATCH] Document Linux's memory barriers

[Alan Cox]

On Maw, 2006-03-07 at 19:10 -0600, Robert Hancock wrote:
> Alan Cox wrote:
> > You must have a strange kernel Andi. Mine marks them as volatile
> > unsigned char * references.
> 
> Well, that and the fact that IO memory should be mapped as uncacheable 
> in the MTRRs should ensure that readl and writel won't be reordered on 
> i386 and x86_64.. except in the case where CONFIG_UNORDERED_IO is 
> enabled on x86_64 which can reorder writes since it uses nontemporal 
> stores..

You need both

real/writel need the volatile to stop gcc removing/reordering the
accesses at compiler level, and the mtrr/pci bridge stuff then deals
with bus level ordering for that CPU.

-
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/