linux-kernel - Re: PCIe device driver question

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Message-ID: <20080730164718.1befdd07@lxorguk.ukuu.org.uk>
Date:	Wed, 30 Jul 2008 16:47:18 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Sanka Piyaratna <cesanka@...oo.com>
Cc:	linux-kernel@...r.kernel.org
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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