Subject: Re: [PATCH v5 2/4] arch: Add lightweight memory barriers dma_rmb() and dma_wmb()

From: Benjamin Herrenschmidt <[email-masked]>
Date: Wed, 26 Nov 2014 10:15:28 +1100

On Tue, 2014-11-18 at 17:24 -0800, Alexander Duyck wrote:
> There are a number of situations where the mandatory barriers rmb() and
> wmb() are used to order memory/memory operations in the device drivers
> and those barriers are much heavier than they actually need to be.  For
> example in the case of PowerPC wmb() calls the heavy-weight sync
> instruction when for coherent memory operations all that is really needed
> is an lsync or eieio instruction.
>  .../...

For powerpc:

Acked-by: Benjamin Herrenschmidt <[email-masked]>