Re: [PATCH 1/2] hwmon: Enhance the sysfs API for power meters.

Darrick J. Wong
2009-08-10T21:12:17Z

On Sat, Aug 08, 2009 at 11:48:30PM +0200, Pavel Machek wrote:
>
> Uhuh. This is hwmon documentation AFAICT; so a) it should be
> documented here, and b) interface should be generic so that it works
> without ACPI, too.

Perhaps it is time to set up a netlink interface for all the hwmon drivers?
>From what I can tell, some of the chips can send interrupts when alarms go off,
though I don't see much of an effort by the drivers to catch those interrupts.
For sure there's no netlink socket that one can read for that sort of thing; a
far as I can tell, client programs are expected to bang on sysfs periodicially
to figure out when things have gone bad.

<shrug> If there's sufficient interest in building a netlink-like notification
system to replace (or augment) polling, I'll put something together.

> > All it really does is generates an ACPI Notify event, which is a hint to the OS
> > that it could re-read the power meter use.
>
> So it is one-shot? Document that.

<nod>

> > The ACPI spec is silent on this matter. It's not clear if the OS is supposed
> > to monitor and take action on its own when power > cap, or if the hardware/BIOS
> > will take action, or possibly both...?
>
> Having user<->kernel interface that is well... uh... undocumented
> makes little sense.

So it goes with ACPI. Given that things like Node Manager and Active Energy
Manager claim to be able to control power use, I would guess that it is
generally likely that a power monitoring system would take action on its own to
cut power use, and not necessarily bothering to tell the OS exactly what it's
doing.

--D