linux-kernel - Re: [PATCH 2/3] dma: override "dma_flags_set

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Message-ID: <46CBE838.4000302@sgi.com>
Date:	Wed, 22 Aug 2007 09:39:36 +0200
From:	Jes Sorensen <jes@....com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	akepner@....com, Randy Dunlap <randy.dunlap@...cle.com>,
	linux-kernel <linux-kernel@...r.kernel.org>, rdreier@...co.com,
	linux-ia64 <linux-ia64@...r.kernel.org>
Subject: Re: [PATCH 2/3] dma: override "dma_flags_set_dmaflush" for sn-ia64

James Bottomley wrote:
> On Tue, 2007-08-21 at 17:34 -0700, akepner@....com wrote:
>> The term "posted DMA" is used to describe this behavior in the Altix 
>> Device Driver Writer's Guide, but it may be confusing things here. 
>> Maybe a better term will suggest itself if I can clarify....
> 
> OK, but posted DMA has a pretty specific meaning in terms of PCI, hence
> the confusion.

Maybe it would be more better to refer to this as 'out of order DMA'?

>> On Altix, DMA from a device isn't guaranteed to arrive in host memory 
>> in the order it was sent from the device. This reordering can happen 
>> in the NUMA interconnect (it's specifically not a PCI reordering.)
> 
> This is mmiowb and read_relaxed() again, isn't it?

I believe it's the same problem, except this time it's when exposing
structures to userland.

Cheers,
Jes
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