linux-kernel - Re: PCIe device driver question

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Date:	Wed, 30 Jul 2008 22:21:37 +0530
From:	"V.Radhakrishnan" <rk@...-labs.com>
To:	Sanka Piyaratna <cesanka@...oo.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: PCIe device driver question


> > 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 ?

V. Radhakrishnan
http://www.atr-labs.com

On Wed, 2008-07-30 at 09:09 -0700, Sanka Piyaratna wrote:
> Hi Alan,
> 
> Actually the failures occur at addresses lot higher than this range, I am noticing the failure at dma address 0x0000000037845000. This would be at around 900MB ?
> 
> Thanks
> 
> Sanka
> 
> 
> 
> ----- Original Message ----
> From: Alan Cox <alan@...rguk.ukuu.org.uk>
> To: Sanka Piyaratna <cesanka@...oo.com>
> Cc: linux-kernel@...r.kernel.org
> Sent: Thursday, 31 July, 2008 1:17:18 AM
> Subject: Re: PCIe device driver question
> 
> On Wed, 30 Jul 2008 09:00:58 -0700 (PDT)
> Sanka Piyaratna <cesanka@...oo.com> wrote:
> 
> > Hi,
> > 
> > I am currently developing a PCIe data capture card hardware and the
> > device drivers to drive this. I have implemented DMA on the data
> > capture and the scatter-gather DMA is implemented in the hardware.  I
> > 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. However, my problem is to dma data to any
> > address less than this. When I try to DMA data to an address less than
> > 0x0000_0001_0000_0000, the hardware device hangs indicating that the
> > address does not exist.
> 
> Assuming the failures are in the range 640K-1MB then I would imagine your
> bridge doesn't permit transfers via DMA to the ISA hole.
> 
> 
> 
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