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Date: Wed, 18 Apr 2012 20:10:11 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, linaro-mm-sig@lists.linaro.org,
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Subject: Re: [PATCH] dma-buf: mmap support
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> How do you ensure that no device can do DMA on the buffer while it's mapped
> into user space in a noncoherent manner?

Why do we want to enforce that ? We provide the appropriate base service
but you need to know what you are doing. In reality a lot of use cases
are going to need far more than a simple kernel API could try and guess
coherency rules about.