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

Bjorn Helgaas
2018-11-07T17:10:44Z

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