linux-kernel - Re: [PATCH] fsldma: add support to 36-bit physical address

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Message-Id: <2C3F2C02-35B6-46AF-82DA-44ACCBFB8362@digitaldans.com>
Date:	Tue, 21 Sep 2010 15:05:05 -0700
From:	Dan Malek <ppc6dev@...italdans.com>
To:	Scott Wood <scottwood@...escale.com>
Cc:	Timur Tabi <timur.tabi@...il.com>, dan.j.williams@...el.com,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fsldma: add support to 36-bit physical address


On Sep 21, 2010, at 2:49 PM, Scott Wood wrote:

>
> On Tue, 21 Sep 2010 16:43:12 -0500
> Timur Tabi <timur.tabi@...il.com> wrote:
>
>> Since we don't DMA the descriptors themselves, I just don't see how
>> this patch does anything.
>
> Look in dmaengine.c, there are calls to dma_map_single() and
> dma_map_page(), using what I assume is that same device pointer --
> unless there's confusion between the channel and the controller.

The DMA descriptors are accessed using DMA by the
controller itself.  The APIs need to ensure proper coherency
between the CPU and the DMA controller for the
descriptor access.  The underlying implementation of the
API will depend upon the hardware capabilities that
ensure this coherency.

	-- Dan

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