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Date: Tue, 04 Dec 2007 17:44:27 -0600
From: Scott Wood <scottwood@freescale.com>
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To: Arnd Bergmann <arnd@arndb.de>
Subject: Re: ucc_uart: add support for Freescale QUICCEngine UART
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Cc: linuxppc-dev@ozlabs.org, Timur Tabi <timur@freescale.com>
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Arnd Bergmann wrote:
> On Wednesday 05 December 2007, Scott Wood wrote:
>>> You can argue that the QS is really a DMA device, but in that
>>> case you should convert the driver to use the DMA mapping
>>> interfaces correctly, which I would consider overkill.
>> Why is it overkill?
>> 
> 
> Well, if the QE can never be used with an IOMMU anyway,

I'm unconvinced that that will always be the case.

> The DMA mapping API is meant for the cases where physical and dma 
> addresses can be different in the first place.

It's also used for noncoherent DMA; while it's unlikely Freescale will 
come out with a QE 8xx chip any time soon, there could be hardware bugs 
or performance considerations that make it desireable to treat it as 
non-coherent.

-Scott