Re: [net-next PATCH RFC 19/26] arch/sparc: Add option to skip DMA sync as a part of map and unmap

[David Miller]

From: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>
Date: Mon, 24 Oct 2016 08:06:07 -0400

> This change allows us to pass DMA_ATTR_SKIP_CPU_SYNC which allows us to
> avoid invoking cache line invalidation if the driver will just handle it
> via a sync_for_cpu or sync_for_device call.
> 
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: sparclinux@xxxxxxxxxxxxxxx
> Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>

This is fine for avoiding the flush for performance reasons, but the
chip isn't going to write anything back unless the device wrote into
the area.