Re: [PATCH] ACPI: battery: register power_supply subdevice even when battery not present

[Anton Vorontsov <avorontsov@ru.mvista.com>]

On Fri, Sep 11, 2009 at 01:28:42PM +0100, Alan Jenkins wrote:
> [CC power_supply maintainers]
> 
> I tried to fix the ACPI battery driver so it created a power supply
> device even if the battery is not present.  All the other battery
> drivers do this.  It would let e.g. gnome-power-manager to detect the
> presence of a battery bay, and allow configuration of battery
> behaviour even when the battery has been removed.

This was discussed several times already.

http://lkml.org/lkml/2009/4/27/314
http://lkml.org/lkml/2007/10/27/170

> Unfortunately this is not as easy as I thought.

And not possible for certain batteries.

[...]
> I can think of some more complex ways to do this
> 
> 1) Destroy and recreate the battery device on hotplug.
> 2) Modify the generic power supply class to allow changing the set of attribute.
> 3) Restructure the interface to provide a "battery bay" device as a parent.
> 
> 1) and 2) are hacks.  1) could at least cause annoyingly spurious UI
> events.  2) sounds like a bad idea, but existing userspace _might_
> handle it because it already happens at registration time.  (Power
> supply attributes aren't available on the initial ADD uevent; they are
> added in a follow-up CHANGE uevent).
> 
> 3) could be backwards compatible and relatively straightforward.  The
> "battery bay" could be a new type of power supply device, with no
> attributes of its own.

Yes, that would be nice. There could be some attributes though,
I can think of a temperature sensor (measures ambient/bay
temperature), a battery presence/lock sensor etc.

IIRC, battery bay in iPaq hx4700 devices can report if a battery is
locked (that's all it can do, but still useful).

> It could be created automatically for non-acpi batteries.

Why? If there is no bay, we don't need any device for it.

Thanks,

-- 
Anton Vorontsov
email: cbouatmailru@gmail.com
irc://irc.freenode.net/bd2