linux-kernel - Re: [PATCH] ACPI / Battery: Return -ENODATA for unknown values in get

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Message-ID: <20101017095940.GA4077@sucs.org>
Date:	Sun, 17 Oct 2010 10:59:40 +0100
From:	Sitsofe Wheeler <sitsofe@...oo.com>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Len Brown <lenb@...nel.org>, Zhang Rui <rui.zhang@...el.com>,
	David Zeuthen <davidz@...hat.com>,
	Richard Hughes <richard@...hsie.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPI / Battery: Return -ENODATA for unknown values in
	get_property()

On Sun, Oct 17, 2010 at 03:19:53AM -0200, Henrique de Moraes Holschuh wrote:
> On Sun, 17 Oct 2010, Rafael J. Wysocki wrote:
> > In fact, the driver is supposed to return -ENODATA in that case, which will
> > result in the read from /sys/class/power_supply/BAT0/current_now
> > fail (I guess upower should be able to cope with that).
>
> ENODATA?  Shouldn't it be ENXIO?  There is no non-blocking data stream
> involved in a sysfs attribute.

Using ENODATA and ENXIO appears to solve the problem (upower reports a
rate of 0.0). However when plugging the battery in after previously only
being on AC power none of the /sys/class/power_supply/BAT0/uevent:*
files are created so upower never realises a battery has been plugged
in. A further issue with ENXIO is is the following repeatedly appears in
dmesg:

power_supply BAT0: driver failed to report `current_now' property

> Of course, the RIGHT thing would be to not expose in sysfs attributes
> that are unsupported by the firmware/hardware in the first place, but
> that's easier said than done.

My understanding is that this very hard to do because you can't tell if
the problem was transient (battery settling) or permanent (feature not
supported).

-- 
Sitsofe | http://sucs.org/~sits/
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