Date: Tue, 28 Aug 2007 13:19:42 +0200
From: Jean Delvare <khali@linux-fr.org>
To: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: "Darrick J. Wong" <djwong@us.ibm.com>,
       "Mark M. Hoffman" <mhoffman@lightlink.com>,
       linux-kernel@vger.kernel.org, lm-sensors@lm-sensors.org
Subject: Re: [lm-sensors] [PATCH] v1 of IBM power meter driver
Message-ID: <20070828131942.18449886@hyperion.delvare>
In-Reply-To: <20070828015029.GA10107@khazad-dum.debian.net>
References: <20070827211446.GG32667@tree.beaverton.ibm.com>
	<20070828015029.GA10107@khazad-dum.debian.net>
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Hi Darrick, hi Henrique,

Good thing that manufacturers start including wattmeters in their
hardware. Hopefully this will help users better control their power
consumption in the long run.

On Mon, 27 Aug 2007 22:50:29 -0300, Henrique de Moraes Holschuh wrote:
> On Mon, 27 Aug 2007, Darrick J. Wong wrote:
> > documentation doesn't mention any naming conventions for sensors that
> > measure Watts, so I am proposing that they be called "powerX_input" in a
> > fashion similar to temperature/rpm/current sensors.  If that is
> > agreeable to everyone, I'll post a follow-up patch to amend the
> > documentation.
> 
> What unit should we use? Watts are way, way too big as there is no
> floating/fixed point in sysfs.  10^-6 W is probably what is called for,
> since we already need 10^-3 V and 10^-3 A.  Small portable devices can
> easily draw less than 10^-3 W nowadays.

Good point. The driver currently exports non-integer values, which is
not acceptable, so indeed it needs to be changed. We want at least a
resolution of 10^-3 W. Not sure about 10^-6 W. I am surprised that
portable devices can really draw less than 1 mW, and be it the case, I
doubt that manufacturers will embed a wattmetter: it would probably
draw more current than the rest of the device ;) so it may not be
relevant for our decision.

So I think I'd go with 10^-3 W, but I welcome diverging opinions. Out
of curiosity, what is the physical resolution of IBM's device?

I see that the driver relies on IPMI. Can't it be merged with the
out-of-tree impisensors driver then? This would give that driver some
momentum so that it can finally be merged, and I would like to avoid
having two drivers if one is enough. Note though that I don't know
anything about IPMI so I might as well be totally wrong ;)

-- 
Jean Delvare
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