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

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Message-ID: <20080304231525.GA25125@suse.de>
Date:	Tue, 4 Mar 2008 15:15:25 -0800
From:	Greg KH <gregkh@...e.de>
To:	Alex Chiang <achiang@...com>, 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

On Tue, Mar 04, 2008 at 03:58:30PM -0700, Alex Chiang wrote:
> * 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.

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
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