linux-kernel - Re: [PATCH v2] Re: Battery class driver.

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Date:	Tue, 31 Oct 2006 15:28:27 +0200
From:	"Shem Multinymous" <multinymous@...il.com>
To:	"Greg KH" <greg@...ah.com>
Cc:	"David Zeuthen" <davidz@...hat.com>,
	"Richard Hughes" <hughsient@...il.com>,
	"David Woodhouse" <dwmw2@...radead.org>,
	"Dan Williams" <dcbw@...hat.com>, linux-kernel@...r.kernel.org,
	devel@...top.org, sfr@...b.auug.org.au, len.brown@...el.com,
	benh@...nel.crashing.org,
	"linux-thinkpad mailing list" <linux-thinkpad@...ux-thinkpad.org>,
	"Pavel Machek" <pavel@...e.cz>, "Jean Delvare" <khali@...ux-fr.org>
Subject: Re: [PATCH v2] Re: Battery class driver.

Hi Greg,

On 10/31/06, Greg KH <greg@...ah.com> wrote:
> > On 10/28/06, David Zeuthen <davidz@...hat.com> wrote:
> > >What about just prepending the unit to the 'threshold' file? Then user
> > >space can expect the contents of said file to be of the form "%d %s". I
> > >don't think that violates the "only one value per file" sysfs mantra.
> >
> > The tp_smapi battery driver did just this  ("16495 mW"). But I dropped
> > it in a recent version when Pavel pointed out the rest of sysfs, hwmon
> > included, uses undecorated integers.
> > Consistency aside, it seems reasonable and convenient. You have to
> > decree that writes to the attributes (where relevant) don't include
> > the units, of course, so no one will expect the kernel to parse that.
> >
> > There's an issue here if a drunk driver decides to specify (say)
> > capacity_remaining in mWh and capacity_last_full in mAa, which will
> > confuse anyone comparing those attributest. So don't do that.
> >
> > Jean, what's your opinion on letting hwmon-ish attributes specify
> > units as "%d %s" where these are hardware-dependent?
>
> No, the sysfs files should just always keep the same units as
> documented.  It's easier all around that way.

It sure is easier, but we're discussinng the case where units change
in runtime; what do we document then? Plug in a different battery and
you get reports in mA and mAh  insted of mW and mWh.

The suggestions so far were:
1. Append units string to the content of such attribute:
   /sys/.../capacity_remaining reads "16495 mW".
2. Add a seprate *_units attribute saying what are units for other attribute:
   /sys/.../capacity_units gives the units for
   /sys/.../capacity_{remaining,last_full,design,min,...}.
3. Append the units to the attribute names:
   capacity_{remaining,last_full,design_min,...}:mV.

  Shem
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