linux-kernel - Re: PCIe device driver question

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Message-ID: <4890BF39.6060608@shaw.ca>
Date:	Wed, 30 Jul 2008 13:21:29 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	"V.Radhakrishnan" <rk@...-labs.com>
CC:	Sanka Piyaratna <cesanka@...oo.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: PCIe device driver question

V.Radhakrishnan wrote:
>>> am testing this in an X86_64 architecture machine with 4 GB of RAM. I
>>> am able to successfully dma data into any memory (dma) address >
>>> 0x0000_0001_0000_0000.
> 
> How can you DMA "successfully" into this address which is > 4 GB when
> you have only 4 GB RAM ? Or am I missing something ?

The MMIO and other reserved memory space at the top of the 32-bit memory 
space will cause the top part of memory to be relocated above 4GB.
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