Re: [PATCH v2 5/7] driver core: Add device location to "struct device" and expose it in sysfs

From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Rajat Jain <rajatja@google.com>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Joerg Roedel <joro@8bytes.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Len Brown <lenb@kernel.org>,
	"open list:AMD IOMMU (AMD-VI)" <iommu@lists.linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux PCI <linux-pci@vger.kernel.org>,
	ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	Raj Ashok <ashok.raj@intel.com>,
	lalithambika.krishnakumar@intel.com,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Prashant Malani <pmalani@google.com>,
	Benson Leung <bleung@google.com>, Todd Broch <tbroch@google.com>,
	Alex Levin <levinale@google.com>,
	Mattias Nissler <mnissler@google.com>,
	Rajat Jain <rajatxjain@gmail.com>,
	Bernie Keany <bernie.keany@intel.com>,
	Aaron Durbin <adurbin@google.com>,
	Diego Rivas <diegorivas@google.com>,
	Duncan Laurie <dlaurie@google.com>,
	Furquan Shaikh <furquan@google.com>,
	Jesse Barnes <jsbarnes@google.com>,
	Christian Kellner <christian@kellner.me>,
	Alex Williamson <alex.williamson@redhat.com>,
	"Oliver O'Halloran" <oohall@gmail.com>,
	Saravana Kannan <saravanak@google.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v2 5/7] driver core: Add device location to "struct device" and expose it in sysfs
Date: Tue, 30 Jun 2020 15:00:34 +0200	[thread overview]
Message-ID: <CAJZ5v0iYFKrouQx_b7afPnz7ohjWOKKDhdHj_3HObKYV_rRhiw@mail.gmail.com> (raw)
In-Reply-To: <20200630125216.GA1109228@kroah.com>

On Tue, Jun 30, 2020 at 2:52 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Tue, Jun 30, 2020 at 01:49:48PM +0300, Heikki Krogerus wrote:
> > On Mon, Jun 29, 2020 at 09:49:41PM -0700, Rajat Jain wrote:
> > > Add a new (optional) field to denote the physical location of a device
> > > in the system, and expose it in sysfs. This was discussed here:
> > > https://lore.kernel.org/linux-acpi/20200618184621.GA446639@kroah.com/
> > >
> > > (The primary choice for attribute name i.e. "location" is already
> > > exposed as an ABI elsewhere, so settled for "site"). Individual buses
> > > that want to support this new attribute can opt-in by setting a flag in
> > > bus_type, and then populating the location of device while enumerating
> > > it.
> >
> > So why not just call it "physical_location"?
>
> That's better, and will allow us to put "3rd blue plug from the left,
> 4th row down" in there someday :)
>
> All of this is "relative" to the CPU, right?  But what CPU?  Again, how
> are the systems with drawers of PCI and CPUs and memory that can be
> added/removed at any point in time being handled here?  What is
> "internal" and "external" for them?
>
> What exactly is the physical boundry here that is attempting to be
> described?

Also, where is the "physical location" information going to come from?

If that is the platform firmware (which I suspect is the anticipated
case), there may be problems with reliability related to that.