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

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Message-ID: <20080304225830.GC3694@ldl.fc.hp.com>
Date:	Tue, 4 Mar 2008 15:58:30 -0700
From:	Alex Chiang <achiang@...com>
To:	Greg KH <gregkh@...e.de>
Cc:	Matthew Wilcox <matthew@....cx>, Gary Hade <garyhade@...ibm.com>,
	kaneshige.kenji@...fujitsu.com, warthog19@...lescrag.net,
	kristen.c.accardi@...el.com, rick.jones2@...com,
	linux-kernel@...r.kernel.org, linux-pci@...ey.karlin.mff.cuni.cz,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 4/4] ACPI PCI slot detection driver

* Greg KH <gregkh@...e.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.

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.

Thanks.

/ac

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