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

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Date:   Wed, 7 Nov 2018 17:40:14 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     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 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.

Guenter