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

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Message-ID: <20200630153816.GD1785141@kroah.com>
Date:   Tue, 30 Jun 2020 17:38:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Rajat Jain <rajatja@...gle.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        "open list:AMD IOMMU (AMD-VI)" <iommu@...ts.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        lalithambika.krishnakumar@...el.com,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Prashant Malani <pmalani@...gle.com>,
        Benson Leung <bleung@...gle.com>,
        Todd Broch <tbroch@...gle.com>,
        Alex Levin <levinale@...gle.com>,
        Mattias Nissler <mnissler@...gle.com>,
        Rajat Jain <rajatxjain@...il.com>,
        Bernie Keany <bernie.keany@...el.com>,
        Aaron Durbin <adurbin@...gle.com>,
        Diego Rivas <diegorivas@...gle.com>,
        Duncan Laurie <dlaurie@...gle.com>,
        Furquan Shaikh <furquan@...gle.com>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Christian Kellner <christian@...lner.me>,
        Alex Williamson <alex.williamson@...hat.com>,
        Oliver O'Halloran <oohall@...il.com>,
        Saravana Kannan <saravanak@...gle.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 5/7] driver core: Add device location to "struct
 device" and expose it in sysfs

On Tue, Jun 30, 2020 at 03:00:34PM +0200, Rafael J. Wysocki wrote:
> On Tue, Jun 30, 2020 at 2:52 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.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?

Who knows?  :)

Some BIOS seem to provide this, but do you trust that?

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

s/may/will/

which means making the kernel inact a policy like this patch series
tries to add, will result in a lot of broken systems, which is why I
keep saying that it needs to be done in userspace.

It's as if some of us haven't been down this road before and just keep
being ignored...

{sigh}

greg k-h