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

Bjorn Helgaas
2018-11-08T13:59:34Z

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