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

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Message-ID: <20181107171044.GA261200@google.com>
Date:   Wed, 7 Nov 2018 11:10:44 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "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>,
        Guenter Roeck <linux@...ck-us.net>, 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>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.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 05:07:07PM +0100, Borislav Petkov wrote:
> On Wed, Nov 07, 2018 at 07:38:56AM -0600, Bjorn Helgaas wrote:
> > Firmware supplies ACPI namespace.  The namespace contains an abstract
> > description of the platform, including devices.  Devices are
> > identified by PNP IDs, which are analogous to PCI vendor/device IDs,
> > except that a device may have several generic "compatible device IDs"
> > in addition to an ID unique to the device.  Devices may also contain
> > methods (supplied by firmware as part of the namespace), which are
> > essentially bytecode that can be executed by the ACPI interpreter in
> > the kernel.  Linux drivers claim ACPI devices based on PNP ID and
> > operate them using either ACPI methods (which can decouple the driver
> > from device specifics) or the usual direct MMIO/IO port/MSR style.
> > 
> > Here's an outline of how it *could* work:
> > 
> >   - AMD defines "AMD0001" device ID for the CPU temp sensor
> >   - BIOS supplies AMD0001 devices in the ACPI namespace
> >   - Each AMD0001 device has a _TMP method (supplied by BIOS and
> >     specific to the CPU)
> >   - Linux driver claims AMD0001 devices
> >   - Driver reads temp sensors by executing _TMP methods (Linux ACPI
> >     interpreter runs the bytecode)
> 
> Thanks for explaining.
> 
> > That way when you release a new platform with different temp sensors,
> > you update the BIOS AMD0001 devices and _TMP methods to know about
> > them, and the old Linux driver works unchanged.
> 
> So I don't know about temp sensors - I'm talking about amd_nb which is
> something... well, I explained already what it is in my previous mail so
> I won't repeat myself.
> 
> Anyway, if there is such a PNP ID device - and I believe I have stumbled
> upon some blurb about it in the BKDGs - which says "this device
> represents the PCI device IDs of a CPU" and if that can be used to
> register amd_nb through it, then sure, I don't see why not.
> 
> This way, when new CPU comes out and the same PNP ID device is present,
> amd_nb would load, sure.

No, the idea was more that that temp monitoring, e.g., k10temp, could
be independent of amd_nb.

But I can tell this idea isn't going anywhere, so let's just forget
that I stuck my neck out and let it die on the vine :)

Bjorn