linux-kernel - Re: [PATCH] 2.6.24-rc1: ensure "present" sysfs attribute even if battery is absent

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Date:	Sat, 27 Oct 2007 21:50:23 +0400
From:	Andrey Borzenkov <arvidjaar@...l.ru>
To:	Alexey Starikovskiy <aystarik@...il.com>
Cc:	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	cbou@...l.ru, dwmw2@...radead.org
Subject: Re: [PATCH] 2.6.24-rc1: ensure "present" sysfs attribute even if battery is absent

On Saturday 27 October 2007, Alexey Starikovskiy wrote:
> Andrey Borzenkov wrote:
> > I am not exactly sure about this one ... what other power_supply class
> > drivers do? Should I fix HAL instead (but then, I do not know whether HAL
> > is the only application that is using this interface).
>
> Hm, do you need separate set of properties for that? You could register
> either of existing two, and read function will not allow read of anything
> but "present". IMHO, this is what other modules do (/drivers/power)

Do they have different set of properties depending on underlying hardware that 
you can't query unless hardware is present? I'd rather avoid adding fake 
attributes; but I do not actually care so which one do you prefer? :)

> One remaining trick here, you need to call unregister/register for
> power_supply if you change attributes -- so please check if your patched
> driver survives insertion of the battery.
>

Neither does your code (nor kpowersave :) ) Remove battery and set of 
attributes is "stuck" instead of being reset to only fixed set of power 
device attributes (basically "info"). The only call to power_supply_register 
is in acpi_battery_add and as far as I can tell this is executed on adding 
*slot* not when content of this slot changes.

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