Date: Tue, 13 Nov 2007 13:21:54 -0700
From: Alex Chiang <achiang@hp.com>
To: Greg KH <greg@kroah.com>
Cc: gregkh@suse.de, kristen.c.accardi@intel.com, lenb@kernel.org,
       matthew@wil.cx, rick.jones2@hp.com, linux-kernel@vger.kernel.org,
       linux-pci@atrey.karlin.mff.cuni.cz,
       pcihpd-discuss@lists.sourceforge.net, linux-acpi@vger.kernel.org
Subject: Re: [PATCH 0/5][RFC] Physical PCI slot objects
Message-ID: <20071113202154.GA22812@ldl.fc.hp.com>
Mail-Followup-To: Alex Chiang <achiang@hp.com>,
	Greg KH <greg@kroah.com>, gregkh@suse.de,
	kristen.c.accardi@intel.com, lenb@kernel.org, matthew@wil.cx,
	rick.jones2@hp.com, linux-kernel@vger.kernel.org,
	linux-pci@atrey.karlin.mff.cuni.cz,
	pcihpd-discuss@lists.sourceforge.net, linux-acpi@vger.kernel.org
References: <20071113000853.GA13341@ldl.fc.hp.com> <20071113170129.GA20185@kroah.com>
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* Greg KH <greg@kroah.com>:
> On Mon, Nov 12, 2007 at 05:08:53PM -0700, Alex Chiang wrote:
> > 
> > Recently, Matthew Wilcox sent out the following mail about
> > PCI slots:
> > 
> >   http://marc.info/?l=linux-pci&m=119432330418980&w=2
> > 
> > The following patch series is a rough first cut at
> > implementing the ideas he outlined, namely, that PCI slots
> > are physical objects that we care about, independent of their
> > hotplug capabilities.
> 
> Also, some companies already provide userspace tools to get all
> of this information about the different slots in a system and
> what is where, from userspace, no kernel changes are needed.
> So, why add all this extra complexity to the kernel if it is
> not needed?

On HP ia64 systems, that information is locked away in ACPI, and
there's no easy way to get at it. Alex Williamson tried providing
a generic dev_acpi driver, so that userspace could do whatever
they wanted to with the information:

  http://lkml.org/lkml/2004/8/3/106

And that effort kinda died. I'm of mixed feelings on that driver,
since it would be really nice to get unfettered access to the
ACPI namespace, but it's pretty dangerous, since any interesting
thing you might want to do is actually a method (aka, it calls
into firmware) and who knows what side effects there might be.

So from my point of view, if ia64 customers want to know about
the slots they have in their systems, we're gonna have to do
something kernel-intrusive anyhow.

Thanks.

/ac

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