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

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Date:   Mon, 24 Oct 2016 14:27:30 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     alexander.h.duyck@...el.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, sparclinux@...r.kernel.org, brouer@...hat.com
Subject: Re: [net-next PATCH RFC 19/26] arch/sparc: Add option to skip DMA
 sync as a part of map and unmap

From: Alexander Duyck <alexander.h.duyck@...el.com>
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@...emloft.net>
> Cc: sparclinux@...r.kernel.org
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>

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.