Plans regarding PECI sensors and PCIe inventory with upstream Linux

Plans regarding PECI sensors and PCIe inventory with upstream Linux

[Paul Fertser]

Hello,

Recently OpenBMC switched to newer Linux version which got upstream
support for the PECI bus, with CPU and DIMM modules temperature
sensors reported via it. I assume this is essential for all
Intel-based server motherboards as monitoring CPU temperature and
spinning fans accordingly is one of the core BMC functionalities.

However, I wasn't able to find[0] any sign that this code can actually
be used in OpenBMC. intelcpusensor daemon exits early as the upstream
code doesn't implement the IOCTLs for direct userspace bus
operations. Is there any work planned to make it compatible, or was
some other way chosen?

Another related question is that peci-pcie daemon used for enumerating
host PCIe devices can no longer be used due to the same reason, is
there some replacement in the works? Where can I track its
development?

[0] https://gerrit.openbmc.org/q/project:openbmc/dbus-sensors+message:intelcpusensor

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Re: Plans regarding PECI sensors and PCIe inventory with upstream Linux

[Winiarska, Iwona]

On Wed, 2023-03-22 at 16:14 +0300, Paul Fertser wrote:
> Hello,
> 
> Recently OpenBMC switched to newer Linux version which got upstream
> support for the PECI bus, with CPU and DIMM modules temperature
> sensors reported via it. I assume this is essential for all
> Intel-based server motherboards as monitoring CPU temperature and
> spinning fans accordingly is one of the core BMC functionalities.
> 
> However, I wasn't able to find[0] any sign that this code can actually
> be used in OpenBMC. intelcpusensor daemon exits early as the upstream
> code doesn't implement the IOCTLs for direct userspace bus
> operations. Is there any work planned to make it compatible, or was
> some other way chosen?

Yes, it's currently not compatible with upstream PECI.

In January there was a thread related to dbus-sensors present and future:
https://lore.kernel.org/openbmc/Y79U52toP0+Y4edh@hatter.bewilderbeest.net/
where Zev mentioned that he started to work on dbus-sensors replacement, which
does support (among other things) upstream PECI:

https://github.com/zevweiss/omnisensor/blob/master/src/peci.rs

> 
> Another related question is that peci-pcie daemon used for enumerating
> host PCIe devices can no longer be used due to the same reason, is
> there some replacement in the works? Where can I track its
> development?

When it comes to pecidev, I didn't plan to have it available upstream.
From my perspective - the uAPI exposed by pecidev is too low-level to be used
for anything other than development purpose. It would also be very tricky to
support certain PECI features reliably (such as wake on peci) in the future if
pecidev was available.

Regarding peci-pcie, the plan would be to, instead of using pecidev, implement a
PECI driver on the kernel side, which exposes the necessary information over
sysfs (abstracting away the PECI commands used internally) and use that in peci-
pcie.

Thanks
-Iwona

> 
> [0]
> https://gerrit.openbmc.org/q/project:openbmc/dbus-sensors+message:intelcpusensor
> 

Re: Plans regarding PECI sensors and PCIe inventory with upstream Linux

[Paul Fertser]

Hello Iwona,

On Fri, Mar 24, 2023 at 09:38:04PM +0000, Winiarska, Iwona wrote:
> On Wed, 2023-03-22 at 16:14 +0300, Paul Fertser wrote:
> > Recently OpenBMC switched to newer Linux version which got upstream
> > support for the PECI bus, with CPU and DIMM modules temperature
> > sensors reported via it. I assume this is essential for all
> > Intel-based server motherboards as monitoring CPU temperature and
> > spinning fans accordingly is one of the core BMC functionalities.
> 
> Yes, it's currently not compatible with upstream PECI.
> 
> In January there was a thread related to dbus-sensors present and future:
> https://lore.kernel.org/openbmc/Y79U52toP0+Y4edh@hatter.bewilderbeest.net/
> where Zev mentioned that he started to work on dbus-sensors replacement, which
> does support (among other things) upstream PECI:
> 
> https://github.com/zevweiss/omnisensor/blob/master/src/peci.rs

It's a rather cool project, but I do not see it having become part of
OpenBMC mainstream just yet. Probably not many have tried even just
testing it, as I only see commits from Zev himself. I hope this will
change in the future.

For now I figured a simple change seems to be enough to allow
IntelCPUSensor from dbus-sensors to continue working on current
OpenBMC:

https://gerrit.openbmc.org/c/openbmc/dbus-sensors/+/62025

> Regarding peci-pcie, the plan would be to, instead of using pecidev, implement a
> PECI driver on the kernel side, which exposes the necessary information over
> sysfs (abstracting away the PECI commands used internally) and use that in peci-
> pcie.

When I was asking about plans I meant something with specific dates,
not just the general outline :) You can see as it currently stands
OpenBMC upstream lost the very essential feature (fan control
depending on CPU temperature) for most (all?) Intel-based servers, so
I'm surprised there's no particular migration path ready in
advance.

That said, thank you for the upstreaming work, I see it was attempted
before for years and you're the one who finally managed to do the
right (from Linux maintainers PoV) thing. Congratulations!

-- 
Be free, use free (http://www.gnu.org/philosophy/free-sw.html) software!
mailto:fercerpav@gmail.com