From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Tue, 15 Feb 2011 15:46:33 +0000
Subject: [RFC] ARM: dma-mapping: outer cache is invalidated twice
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On Tue, Feb 15, 2011 at 04:11:09PM +0100, Per Forlin wrote:
> True. In my case write back is disable but read back is enable, that's
> why I didn't consider it.

What do you mean "write back is disable" ?  You can only prevent
writebacks by using a write-through cache.

Any writeback cache, whether in read-allocate or read-write-allocate
mode will have writebacks.

> Do you think it is feasible to let dma-mapping detect the cache
> configurations in runtime in order to prevent "unnecessary" cache
> operations?

Let's first straighten out your cache understanding above, because I
don't think you understand properly yet.