From: Scott Wood <scottwood@freescale.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linuxppc-dev@ozlabs.org, Timur Tabi <timur@freescale.com>
Subject: Re: ucc_uart: add support for Freescale QUICCEngine UART
Date: Tue, 04 Dec 2007 17:44:27 -0600 [thread overview]
Message-ID: <4755E65B.3050208@freescale.com> (raw)
In-Reply-To: <200712050039.39153.arnd@arndb.de>
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
next prev parent reply other threads:[~2007-12-04 23:44 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-04 17:51 ucc_uart: add support for Freescale QUICCEngine UART Timur Tabi
2007-12-04 22:13 ` Arnd Bergmann
2007-12-04 22:33 ` Timur Tabi
[not found] ` <200712050037.11489.arnd@arndb.de>
2007-12-05 17:06 ` Timur Tabi
2007-12-04 22:39 ` Timur Tabi
2007-12-04 23:26 ` Arnd Bergmann
2007-12-04 23:32 ` Scott Wood
2007-12-04 23:39 ` Arnd Bergmann
2007-12-04 23:44 ` Scott Wood [this message]
2007-12-04 23:47 ` Timur Tabi
2007-12-04 23:56 ` Arnd Bergmann
2007-12-05 0:59 ` Vitaly Bordug
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