On 8/19/2018 11:21 AM, Arnd Bergmann wrote:
This matches my understanding of mmiowb. In fact, mmiowb is a powerpc
thing. All other architectures stub out.
There are a few architectures that define mmiowb to something other
than a nop: some ia64, some mips and sh in particular, plus also the
new riscv.
It does make some sense that alpha might need a barrier between
an mmio store and a spin_unlock, but it was decided earlier to make
that barrier implied by the writel() function rather than require an
explicit mmiowb after it.
I see. When I talked to PowerPC guys a couple of months ago, they told
me that they keep a dirty flag to keep track of mmiowb() required
condition on each writel() execution.
If the dirty flag is set; they issue the mmiowb() inside the
spin_unlock() function.
Sounds like we need a similar solution for all architectures that
require mmiowb().
