linux-kernel - Re: [PATCH] fsldma: use PCI Read Multiple command

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Message-ID: <ed82fe3e0904270731g2d2519a7mc12e4152c716c0a9@mail.gmail.com>
Date:	Mon, 27 Apr 2009 09:31:12 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Liu Dave-R63238 <DaveLiu@...escale.com>
Cc:	Ira Snyder <iws@...o.caltech.edu>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org, Dan Williams <dan.j.williams@...el.com>,
	Li Yang-R58472 <LeoLi@...escale.com>,
	Zhang Wei <wei.zhang@...escale.com>
Subject: Re: [PATCH] fsldma: use PCI Read Multiple command

On Mon, Apr 27, 2009 at 4:09 AM, Liu Dave-R63238 <DaveLiu@...escale.com> wrote:

> You are assuming the PCI memory space is prefetchable( no side effect)
> for DMA.
> Is it possible that DMA is from non-prefetchable memory space?

This should be a safe assumption for this driver.  Remember, this
driver just does offload memcpy, from one region to another.  So the
PCI memory that you are reading from should be just a buffer of data,
and there should be side-effect of reading it.

However, I would like to see a comment at the top of the file warning
people that copying from PCI memory will result in prefetched reads.

-- 
Timur Tabi
Linux kernel developer at Freescale
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