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SubjectRE: Specifying properly the PCI driver model on all linux archite
Date
Alan Cox [mailto:alan@lxorguk.ukuu.org.uk] wrote:
> > I think you will find that you'll have problems with your
> hot swap and
> > bridges, it really should be the PCI subsystem that decides
> what areas of
> > PCI are used or not. Once it is put in the configuration
> register, that
> > should be the end of it.
> >
> > I think that having all the PCI device drivers do
> check_mem_region() and
> > request_mem_region() is going to cause problems.
>
> The memory regions have three states so I think we are ok. They can be
>
> 1. Unused
> 2. Allocated but not used (eg PCI but no driver loaded)
> 3. Used
>
> As you clearly realise the major issue is getting type #1
> right so that
> hot swap devices, AGP gart and the like can grab a hole

Actually, I was thinking the major issue was correctly handling alignment
constraints on PCI-PCI Bridges (PPB) that may exist behind the hot-swap. You
have to have the PPB addresses aligned on a 1MByte boundardary, and they can
nest. You make a PPB hot-swappable, all of the sudden you have a bunch of
cards which come in all at the same time behind the bridge and have to be
allocated out of unused, contiguous space with a minimal address granularity
of 1MBytes.

Is there anything preventing a PCI expansion unit from being hot-swappable?
I haven't had a chance to read the hot-swap PCI specification, so I don't
know off the top of my head. It should be possible.

-Bret

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