Subject: Re: Intel gigabit card with wm driver
To: Allen Briggs <email@example.com>
From: Greg A. Woods <firstname.lastname@example.org>
Date: 01/13/2005 03:46:27
[ On Wednesday, January 12, 2005 at 11:06:16 (-0500), Allen Briggs wrote: ]
> Subject: Re: Intel gigabit card with wm driver
> On Wed, Jan 12, 2005 at 03:03:35AM -0500, Greg A. Woods wrote:
> > I've been trying verious models of Intel PRO 1000 cards on an
> > AlphaServer ES40 running NetBSD.
> > I haven't had a whole lot of luck getting them to really perform
> > properly, but apparently that's due do deficiencies in the way the DMA
> > is handled for the alpha when there's a lot of physical memory present
> > (the system has a mere 16GB of RAM, half its maximum :-)
> That's largely to deal with 32-bit PCI trying to access a >32-bit
> address space, right?
That's what I would have assumed....
> Assuming that's the case, it seems like there should be a way around
> using bounce buffers for cards that do have 64-bit address support.
> Does the alpha PCI bus have direct access to all of physical RAM?
Yes, sort of, I think. The 21272 chipset (Typhoon revision in the ES40
model 2) uses window registers (five windows per P-chip) to translate
PCI memory address space into system address space, and is also capable
of doing scatter-gather-mapped DMA. There's also a "monster window"
which apparently direct-maps PCI address bits 34:0 (presumably 35:0 for
Typhoon revisions) to the same system memory address bits with no window
offset. The latter is what I would assume is used for full 64-bit PCI
My understanding is that NetBSD's bus_dma(9) does implement all the
features necessary to make full use of this chipset, including the
scatter-gather capability, though I'm not sure about the "monster
window", but of course it's just another form of direct-mapped DMA.
At least that's what I guess after reading Jason's "A Machine-
Independent DMA Framework for NetBSD" paper a few times through and
after skimming through the 21272 chipset hardware reference manual.
I can't say I have any firm grasp of all the details though! ;-)
Greg A. Woods
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