netdev - Re: [PATCH RFC v5] net: add PCINet driver

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Message-ID: <20090115165359.GA2230@ovro.caltech.edu>
Date:	Thu, 15 Jan 2009 08:54:00 -0800
From:	Ira Snyder <iws@...o.caltech.edu>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	shemminger@...tta.com, netdev@...r.kernel.org
Subject: Re: [PATCH RFC v5] net: add PCINet driver

On Thu, Jan 15, 2009 at 01:58:33PM +0100, Arnd Bergmann wrote:
> On Thursday 15 January 2009, Ira Snyder wrote:
> 
> > The only problem with that is that you cannot route interrupts from the
> > DMA controller over PCI with the PowerPC core running. Which makes it
> > mostly useless for this case.
> 
> If the host supports MSI, you can simply program the DMA controller to
> write the correct message to the inbound address of the MSI interrupt
> controller!
> 
> All modern host systems should have MSI, as this is required by the
> PCIe specification, but it still somewhat limits the choice of your
> hosts.
> 

These are PCI boards, not PCIe. The host computers are all Pentium3-M
systems. I tried enabling MSI on the Freescale boards in the driver, by
calling pci_enable_msi() during probe(), and it failed. I'm pretty sure
I can't do MSI.

I'll keep thinking about how to manage the DMA. Feel free to toss around
any ideas you have, though.

Ira
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