Re: [PATCH v11 01/10] devicetree: power: Add battery.txt

[Sebastian Reichel <sre-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

[-- Attachment #1: Type: text/plain, Size: 4789 bytes --]

Hi,

On Fri, Apr 07, 2017 at 12:23:29PM -0700, Liam Breck wrote:
> [+CC Tony Lindgren]
> 
> Rob & Sebastian & Tony & Andrew,
> 
> With this binding we allow a DT to hard-code battery characteristics.
> But mainline dts files for boards & boxes really should NOT include
> immutable battery properties unless the battery is inseparable from
> the electronics. We want to prevent unpredictable behavior due to
> incorrect DT properties after a user changes a battery to a different
> type.
> 
> It's OK for device vendors to hard-code battery characteristics in DT,
> but mainline dts is another matter.
> 
> If this is agreed, how should we document it?

That's not a problem of mainline vs vendor. The binding may only be
used for batteries, that cannot be exchanged with a different type.
That's why I originally suggested the "fixed-battery" name. IMHO
it would be ok to use the binding also for DTS files distributed
with the mainline kernel as long as the described device provides
some kind of protection against using batteries of a different type.

For example I would feel ok adding a simple-battery node for the
Droid 4 (which probably does not need one), since the battery has
a custom form-factor, is screwed to the device and has a custom
connector. So while it can be replaced, the new battery would have
the same technical specs.

I suggest to add something similar as the following to the binding:

Using incorrect battery parameters is a SAFETY HAZARD - If used
incorrectly, Lithium based batteries can explode. You should be
really sure, that all provided values are correct. Also if the
battery in your device can be replaced with a different battery
(without major hacks), you may not use this binding for safety
reasons.

-- Sebastian

> On Mon, Mar 20, 2017 at 2:43 AM, Liam Breck <liam-RYWXG+zxWwBdeoIcmNTgJF6hYfS7NtTn@public.gmane.org> wrote:
> > From: Liam Breck <kernel-RYWXG+zxWwBdeoIcmNTgJF6hYfS7NtTn@public.gmane.org>
> >
> > Documentation of static battery characteristics that can be defined
> > for batteries which cannot self-identify. This information is required
> > by fuel-gauge and charger chips for proper handling of the battery.
> >
> > Cc: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> > Cc: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> > Signed-off-by: Matt Ranostay <matt-sk+viVC6FLCDq+mSdOJa79kegs52MxvZ@public.gmane.org>
> > Signed-off-by: Liam Breck <kernel-RYWXG+zxWwBdeoIcmNTgJF6hYfS7NtTn@public.gmane.org>
> > ---
> >  .../devicetree/bindings/power/supply/battery.txt   | 43 ++++++++++++++++++++++
> >  1 file changed, 43 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/power/supply/battery.txt
> >
> > diff --git a/Documentation/devicetree/bindings/power/supply/battery.txt b/Documentation/devicetree/bindings/power/supply/battery.txt
> > new file mode 100644
> > index 0000000..53a68c0
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/power/supply/battery.txt
> > @@ -0,0 +1,43 @@
> > +Battery Characteristics
> > +
> > +The devicetree battery node provides static battery characteristics.
> > +In smart batteries, these are typically stored in non-volatile memory
> > +on a fuel gauge chip. The battery node should be used where there is
> > +no appropriate non-volatile memory, or it is unprogrammed/incorrect.
> > +
> > +Required Properties:
> > + - compatible: Must be "simple-battery"
> > +
> > +Optional Properties:
> > + - voltage-min-design-microvolt: drained battery voltage
> > + - energy-full-design-microwatt-hours: battery design energy
> > + - charge-full-design-microamp-hours: battery design capacity
> > +
> > +Battery properties are named, where possible, for the corresponding
> > +elements in enum power_supply_property, defined in
> > +https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/power_supply.h#n86
> > +
> > +Batteries must be referenced by chargers and/or fuel-gauges
> > +using a phandle. The phandle's property should be named
> > +"monitored-battery".
> > +
> > +Example:
> > +
> > +       bat: battery {
> > +               compatible = "simple-battery";
> > +               voltage-min-design-microvolt = <3200000>;
> > +               energy-full-design-microwatt-hours = <5290000>;
> > +               charge-full-design-microamp-hours = <1430000>;
> > +       };
> > +
> > +       charger: charger@11 {
> > +               ....
> > +               monitored-battery = <&bat>;
> > +               ...
> > +       };
> > +
> > +       fuel_gauge: fuel-gauge@22 {
> > +               ....
> > +               monitored-battery = <&bat>;
> > +               ...
> > +       };
> > --
> > 2.9.3
> >

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]