On Thu, 2014-05-22 at 17:47 +0100, Will Deacon wrote: > A corollary to this is that mmiowb() probably needs rethinking. As it > currently > stands, an mmiowb() is required to order MMIO writes to a device from multiple > CPUs, even if that device is protected by a lock. However, this isn't often > used > in practice, leading to PowerPC implementing both mmiowb() *and* synchronising > I/O in spin_unlock. > > I would propose making the non-relaxed I/O accessors ordered with respect to > LOCK/UNLOCK, leaving mmiowb() to be used with the relaxed accessors, if > required, but would welcome thoughts/suggestions on this topic.
I agree on the proposed semantics, though for us that does mean we still need that per-cpu flag tracking non-relaxed MMIO stores and corresponding added barrier in unlock. Eventually, if the use of the relaxed accessors becomes pervasive enough I suppose I can just make the ordered ones unconditionally do 2 barriers. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
