Re: [patch] pci: revert "PCI: remove transparent bridge sizing"

From: Benjamin Herrenschmidt
Date: Wed Mar 26 2008 - 19:06:31 EST



On Wed, 2008-03-26 at 15:47 -0700, Linus Torvalds wrote:
> > I was talking about IO not memory mostly here.
>
> Yeah, low IO is also reserved on PC's (the low 256 IO ports are
> motherboard resources and contain stuff like legacy DMA channel setup
> etc)

Sure but can't that be in a kind of southbridge ? Like HT or PCIe
segment out of the CPU gets through a virtual P2P wich then hits the
"legacy" combo blob masquerading as a PCI device ? I remember seeing
that sort of thing in the past and I -think- it was some kind of x86
chipset hijacked on powerpc...

> You could imagine having it behind a PCI bridge, but in practice it's
> always on the NB/SB (and if you want to support some of the odder
> things
> like the NMI reason and the i387 error ports, they pretty much have
> to
> be - it would be insane to make a special PCI chips on a separate bus
> that does things like that).

It's often all virtual inside a single chip.

Anyway, doesn't matter much at this stage I suppose, but it would be
nice to not use 0 as meaning invalid when sizing bridge windows and I'm
not sure at all about using "start" as an alignment indicator neither...
It will be much over-aligned in some cases, adding constraints to the
allocator where we didn't have any before no ?

Ben.


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