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

Borislav Petkov
2018-11-07T16:07:07Z

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.

Maybe Brian knows more on the subject...

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.