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

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Message-ID: <20090115233131.GE9091@ovro.caltech.edu>
Date:	Thu, 15 Jan 2009 15:31:31 -0800
From:	Ira Snyder <iws@...o.caltech.edu>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linuxppc-dev@...abs.org, Jan-Bernd Themann <themann@...ibm.com>,
	netdev@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org, shemminger@...tta.com,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH RFC v5] net: add PCINet driver

On Thu, Jan 15, 2009 at 11:53:24PM +0100, Arnd Bergmann wrote:
> On Thursday 15 January 2009, Ira Snyder wrote:
> > I do have mailboxes (two inbound, two outbound) which can generate
> > interrupts, as well as doorbell registers (one inbound, one outbound).
> > The doorbell register's bits are "write 1 to clear", and can only be
> > cleared by the opposite side.
> > 
> 
> Ok, in this case, you should be able to use one of these to implement
> the DMA complete interrupt, but adding an extra DMA transfer to the
> mailbox after each transfer that you want to get notified for.

Yep. I wouldn't have come up with that idea on my own, but it seems
obvious now :)

It seems a little strange to keep the DMA descriptors host memory (the
DMA controller will need to issue a PCI read to get them) but I guess
that is how real network cards work.

Thanks,
Ira
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