Re: RFC: Changes for PCI

From: Tom Gall (
Date: Thu Jun 28 2001 - 16:11:31 EST

Gérard Roudier wrote:
> On Wed, 27 Jun 2001, Jeff Garzik wrote:
> > Tom Gall wrote:
> > > Well you have device drivers like the symbios scsi driver for instance that
> > > tries to determine if it's seen a card before. It does this by looking at the
> > > bus,dev etc numbers... It's quite reasonable for two different scsi cards to be
> > > on the same bus number, same dev number etc yet they are in different PCI
> > > domains.
> > >
> > > Is this a device driver bug or feature?
> >
> > I hesitate to call it a device driver bug, because that was likely the
> > best decision Gerard could make at the time.
> >
> > However, I think the driver (only going by your description) would be
> > more correct to use a pointer to struct pci_dev. We have a token in the
> > kernel that is guaranteed 100% unique to any given PCI device: the
> > pointer to its struct pci_dev.
> The driver checks against PCI bus+dev+func in 2 situations:
> 1) To apply the boot order that user can set up in the controller NVRAMs.
> 2) To detect buggy double reporting of the same device by the kernel PCI
> code (this made lot of troubles at some time).

Thanks much for the clarification. Do you still battle buggy double reporting?
Has this been fixed? Is it a bug on some specific architecture?
> The great bug is to invent useless abstractions that don't match reality.
> Such brain masturbation leads to confusion (hence subtle bugs) and
> useless software bloatage (thus _real_ resource wastage).

Agreed. (A couple of my posts last night didn't make it through... appears that isn't set up entirely right for ENC)

> If we want to handle _real_ PCI bus domains, we just have to add a domain
> number to identify a _real_ PCI device. Anything that wants to hide such
> reality in some opaque data looks like brain masturbation to me.

Again also agreed. Now I'm REALLY anxious for 2.5 8-)

> Gérard.



Tom Gall - PPC64 Maintainer      "Where's the ka-boom? There was
Linux Technology Center           supposed to be an earth
(w)         shattering ka-boom!"
(w) 507-253-4558                 -- Marvin Martian
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