linux-kernel - Re: [PATCH 2/4] x86/amd_nb: add support for newer PCI topologies

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Message-ID: <20181108135934.GD41183@google.com>
Date:   Thu, 8 Nov 2018 07:59:34 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        "Woods, Brian" <Brian.Woods@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Clemens Ladisch <clemens@...isch.de>,
        Jean Delvare <jdelvare@...e.com>, Pu Wen <puwen@...on.cn>,
        Jia Zhang <qianyue.zj@...baba-inc.com>,
        Takashi Iwai <tiwai@...e.de>,
        Andy Whitcroft <apw@...onical.com>,
        Colin Ian King <colin.king@...onical.com>,
        Myron Stowe <myron.stowe@...hat.com>,
        Sumeet Pawnikar <sumeet.r.pawnikar@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 2/4] x86/amd_nb: add support for newer PCI topologies

On Wed, Nov 07, 2018 at 05:40:14PM -0800, Guenter Roeck wrote:
> On 11/7/18 3:14 PM, Bjorn Helgaas wrote:
> > 
> > > 
> > > There is no INT3401 on any newer atom or core platforms, so you can't
> > > enumerate on this device. We don't control what ACPI device is present
> > > on a system. It depends on what the other non-Linux OS is using.
> > 
> > Sure, you can't *force* OEMs to supply a given ACPI device, but you
> > can certainly say "if you want this functionality, supply INT3401
> > devices."  That's what you do with PNP0A03 (PCI host bridges), for
> > example.  If an OEM doesn't supply PNP0A03 devices, the system can
> > boot just fine as long as you don't need PCI.
> > 
> > This model of using the PCI IDs forces OS vendors to release updates
> > for every new platform.  I guess you must have considered that and
> > decided whatever benefit you're getting was worth the cost.
> > 
> 
> I really dislike where this is going. Board vendors - and that included
> Intel when Intel was still selling boards - have a long history of only
> making mandatory methods available in ACPI. Pretty much all of them don't
> make hardware monitoring information available via ACPI. This is a pain
> especially for laptops where the information is provided by an embedded
> controller. On systems with Super-IO chips with dedicated hardware
> monitoring functionality, they often go as far as signing mutual NDAs
> with chip vendors, which lets both the board and the chip vendor claim
> that they can not provide chip specifications to third parties, aka
> users.
> 
> You are pretty much extending that to CPU temperature monitoring. The
> fallout, if adopted, will be that it will effectively no longer be
> possible to monitor the temperature on chips supporting this
> "feature".
> 
> I do not think that would be a good idea.

I wasn't aware of these political implications.  Thanks for raising
them.

I'm not in a position to balance those implications vs the technical
question of minimizing the burden of supporting new platforms, so I'll
try again to bow out of this.

Bjorn