linux-kernel - Re: [RFC] ARM DMA mapping TODO, v1

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Message-ID: <20110428094215.GW17290@n2100.arm.linux.org.uk>
Date:	Thu, 28 Apr 2011 10:42:15 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Arnd Bergmann <arnd@...db.de>, linaro-mm-sig@...ts.linaro.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC] ARM DMA mapping TODO, v1

On Thu, Apr 28, 2011 at 07:31:06AM +1000, Benjamin Herrenschmidt wrote:
> The question remains, if we ever want to do more complex demand-paged
> operations, should we also expose a lower level set of functions to get
> struct page out of a dma_alloc_coherent() allocation and to get the
> pgprot for the user dma mapping ?

I don't think so - that places the requirement that dma_alloc_coherent()
must be backed by memory with a set of struct page, which may not always
be the case.

Think about dma_alloc_coherent() with dma_declare_coherent_memory() used
with memory which is not part of system RAM.
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