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

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Message-ID: <49F6187F.8020703@ovro.caltech.edu>
Date:	Mon, 27 Apr 2009 13:41:35 -0700
From:	David Hawkins <dwh@...o.caltech.edu>
To:	Timur Tabi <timur@...escale.com>
CC:	Liu Dave-R63238 <DaveLiu@...escale.com>,
	Ira Snyder <iws@...o.caltech.edu>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH] fsldma: use PCI Read Multiple command

Hi Timur,

>> PRC_RM - PCI read multiple
>>    The default PCI read command used by the DMA controller is
>>    PCI Read (PCI command 6h). When the burst length is 32-bytes
>>    or longer, PCI Read Line (PCI command Eh) is used (undocumented
>>    feature of the controller). Using PCI read multiple
>>    (PCI command Ch) results in high-performance across PCI
>>    bridges. DMA transfers to non-prefetchable PCI registers
>>    should not result in prefetched reads, even when using
>>    the PCI read multiple command.
> 
> I was thinking more along the lines of:
> 
> "This driver tells the DMA controller to use the PCI Read Multiple
> command, instead of the PCI Read Line command, for PCI read operations.
>  Please be aware that this setting may result in read pre-fetching on
> some platforms."

Ok, thanks.

Ira will add your comment to the body of the code near
the PRC_RM command and submit a new patch.

Cheers,
Dave

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