linux-kernel - Re: Thermal kernel events API to userspace - Was: Re: thermal: Avoid CONFIG

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Message-Id: <201101251112.28340.trenn@suse.de>
Date:	Tue, 25 Jan 2011 11:12:28 +0100
From:	Thomas Renninger <trenn@...e.de>
To:	Zhang Rui <rui.zhang@...el.com>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	"R, Durgadoss" <durgadoss.r@...el.com>,
	"jdelvare@...ell.com" <jdelvare@...ell.com>,
	Len Brown <lenb@...nel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Kay Sievers <kay.sievers@...y.org>,
	"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-trace-users@...r.kernel.org" 
	<linux-trace-users@...r.kernel.org>
Subject: Re: Thermal kernel events API to userspace - Was: Re: thermal: Avoid CONFIG_NET compile dependency

On Tuesday, January 25, 2011 08:57:49 AM Zhang Rui wrote:
> On Tue, 2011-01-25 at 00:07 +0800, Henrique de Moraes Holschuh wrote:
> > On Mon, 24 Jan 2011, Thomas Renninger wrote:
> > > I wonder whether netlink is the way to go for thermal
> > > events at all.
> > > Sending an udev event would already contain the sysfs
> > > path to the thermal device. A variable which thermal event
> > > got thrown could get added and userspace can read out the rest
> > > easily from sysfs files. But I expect udev is not intended
> > > for such general events?
> > 
> > udev is heavyweight in the userspace side, we'd be much better off using the
> > ACPI event interface (which is netlink), or a new one to deliver system
> > status events, instead of continously abusing udev for this stuff.
> > 
> > > > > Also, the thermal_aux0 and _aux1, we can use the final format specified by you.
> > > > > enum events {
> > > > >  	THERMAL_CRITICAL,
> > > > >  	/* user defined thermal events */
> > > > >  	THERMAL_USER_AUX0,
> > > > >  	THERMAL_USER_AUX1,
> > > > >  	THERMAL_DEV_FAULT,
> > > > >  };
> > 
> > Please give us at least two levels of thermal alarm: critical and emergency
> > (or warning and critical -- it doesn't matter much, as long as there are at
> > least two levels, and which one comes first is defined by the
> > specification).  I'd have immediate use for them on thinkpads.
What kind of thinkpad specific events are these and what actions
should be taken if they happen?
 
> > It is probably best to have three levels (warning, critical, emergency).
> > Best not to tie the API/ABI to the notion of "too hot", one can also alarm
> > when it starts to get to cold.
> > 
> when it's the "too hot" case, what kind of action should be taken upon
> the warning/critical/emergency events?
> I mean what's the difference between these three levels.
I could imagine there is quite some HW out there
with quite different thermal events.
What other actions userspace would take beside logging the event,
telling the user that a fan is switched on, CPU or whatever device
gets throttled. Logging such specific info can only be implemented
in the driver itself and would get lost when exporting things through
a generic thermal interface.

I wonder which events would need userspace to take specific
(configured) actions at all and what kind of action it could be.

What is THERMAL_USER_AUX0?
When will it get thrown and what is userspace expected to do?

    Thomas
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