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

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Date:	Sat, 23 Oct 2010 16:36:37 +0100
From:	Sitsofe Wheeler <sitsofe@...oo.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	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 Sat, Oct 23, 2010 at 12:19:13AM +0200, Rafael J. Wysocki wrote:
> 
> OK, so can you test the patch below, please?

The latest patch seems to fix/workaround the problem. upower now reports
0 as the energy rate, there are no warnings in dmesg and battery hotplug
works. Looks good and there's the option for a future upower to
interpret the missing sysfs as meaning "unknown".

Tested-by: Sitsofe Wheeler <sitsofe@...oo.com>

> The function acpi_battery_get_property() is called by the
> power supply framework's function power_supply_show_property()
> implementing the sysfs interface for power supply devices as the
> ACPI battery driver's ->get_property() callback.  Thus it is supposed
> to return error code if the value of the given property is unknown.
> Unfortunately, however, it returns 0 in those cases and puts a
> wrong (negative) value into the intval field of the
> union power_supply_propval object provided by
> power_supply_show_property().  In consequence, wron negative

wron -> wrong?

> Fix this by making acpi_battery_get_property() return -ENODEV
> for properties with unknown values (-ENODEV is returned, because
> power_supply_uevent() returns with error for any other error code
> returned by power_supply_show_property()).

OK that's sneaky and clever - technically power_supply_uevent should be
more robust but presumably things are already prepared to handle -ENODEV
so overloading the meaning leads to the smallest change.

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