Re: [PATCH 4/4] ACPI PCI slot detection driver

Greg KH
2008-03-04T23:15:50Z

On Tue, Mar 04, 2008 at 03:58:30PM -0700, Alex Chiang wrote:
> * Greg KH <gregkh@suse.de>:
> > On Sat, Mar 01, 2008 at 07:43:07AM -0700, Matthew Wilcox wrote:
> > > On Fri, Feb 29, 2008 at 09:25:42PM -0800, Greg KH wrote:
> > > > What is the guarantee that the names of these slots are correct
>
> No guarantee there. We report whatever firmware tells us.
>
> > > > and do not happen to be the same as the hotpluggable ones?
>
> Stronger guarantee here, since both pci_slot and <foo>hp driver
> will be getting the name of the slot from the same place.
>
> > > That would be a bug -- and yes, bugs happen, and we have to deal with
> > > them.
> >
> > My main concern is that BIOS vendors will not fix these bugs, as no
> > other OS cares/does this kind of thing today. The ammount of bad
> > information out there might be quite large, and I think this was
> > confirmed by some initial testing of IBM systems, right?
>
> We saw problems on Fujitsu machines, where they return an error
> code when the _SUN method is called on a slot that exists in the
> namespace but isn't actually present.
>
> After discussing with Kenji-san about specs, we came to the
> agreement that he was ok with this behavior because he had the
> option to not load pci_slot on his machines.
>
> I agree that there might be lots of buggy firmwares out there,
> but we won't know for certain until we get some exposure. And I
> think the upside is worth it.
>
> Kristen suggested the linux-next tree. That sounds viable to
> me...
>
> > > > Why show this information on machines that can not do
> > > > anything with these slots at all? Will that not just
> > > > confuse people?
> > >
> > > Only for people who think that /sys/bus/pci/slots/ is for
> > > hotpluggable slots only. There is plenty of useful
> > > information available for slots that aren't hotpluggable (eg
> > > bus address, speed, width, error status).
> >
> > Can the userspace tools that are using the existing directories
> > thinking that only hotplug slots are there, handle
> > "non-hotplug" slots showing up in this location?
>
> Of course we shouldn't break userspace, no one wants that. But
> nothing about that name (/sys/bus/pci/slots/) implies "hotplug
> only", and we have no idea how big the problem might be.

But that is what the current code does, so I know a lot of userspace
programs assume that all slots there are valid hotplug slots.

I know I sure don't want to go fix up a lot of horrible Java
closed-source code in IBM's huge system management toolkits :(

> Again, I'm thinking more exposure in linux-next might be a
> reasonable way for us to figure out how bad (or good) the
> situation might really be out there.

Ok, care to resend them with the requested updates?

thanks,

greg k-h