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

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Date:	Mon, 10 Aug 2009 14:12:11 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Len Brown <lenb@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	lm-sensors <lm-sensors@...sensors.org>,
	linux-acpi <linux-acpi@...r.kernel.org>,
	Zhang Rui <rui.zhang@...el.com>
Subject: Re: [PATCH 1/2] hwmon: Enhance the sysfs API for power meters.

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
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