linux-kernel - Re: [PATCH 0/3] pci: let devices flush DMA to host memory

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Message-ID: <20070827222027.GD29161@sgi.com>
Date:	Mon, 27 Aug 2007 15:20:27 -0700
From:	akepner@....com
To:	Grant Grundler <grundler@...isc-linux.org>
Cc:	linux-kernel@...r.kernel.org, linux-pci@...ey.karlin.mff.cuni.cz,
	gregkh@...e.de,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Jes Sorensen <jes@....com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH 0/3] pci: let devices flush DMA to host memory

On Mon, Aug 27, 2007 at 04:05:48PM -0600, Grant Grundler wrote:

> .....
> After reading the thread, my take is we need a more elegant way for a
> device driver to handle registration of DMA regions allocated by user
> space. The API would "make this page/region act like dma_alloc_coherent()".
> That implies strong ordering between CPU and DMA to/from the device.
> Maybe the code is the right thing and I want a name that makes
> sense in the context of current DMA API.

Need to think about this...

> 
> On IRC, willy suggested an mmap() flag and that sounds reasonable too
> though I don't know if it's feasible. 
> 

Yeah, we're doing something like this now as a band-aid solution. 
Not a flag to mmap(), but a magic offset value. But it wasn't 
acceptable to the maintainer of the mthca IB driver (Roland 
Dreier), hence the new proposal....

-- 
Arthur

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