Date:	Tue, 8 Sep 2015 21:26:18 -0500
From:	Andreas Dannenberg <dannenberg@...com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
CC:	Ramakrishna Pallala <ramakrishna.pallala@...el.com>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	<devicetree@...r.kernel.org>, Sebastian Reichel <sre@...nel.org>,
	Jenny TC <jenny.tc@...el.com>
Subject: Re: [PATCH] power: bq24261_charger: Add support for TI BQ24261
 charger

On Mon, Sep 07, 2015 at 12:57:56PM +0900, Krzysztof Kozlowski wrote:
> 2015-09-07 2:23 GMT+09:00 Ramakrishna Pallala <ramakrishna.pallala@...el.com>:
> >
> > Add new charger driver support for BQ24261 charger IC.
> >
> > BQ24261 charger driver relies on extcon notifications to get the
> > charger cable type and based on that it will set the charging parameters.
> >
> > Signed-off-by: Ramakrishna Pallala <ramakrishna.pallala@...el.com>
> > Signed-off-by: Jennt TC <jenny.tc@...el.com>
> > ---
> >  .../devicetree/bindings/power/bq24261.txt          |   37 +
> >  drivers/power/Kconfig                              |    6 +
> >  drivers/power/Makefile                             |    1 +
> >  drivers/power/bq24261_charger.c                    | 1208 ++++++++++++++++++++
> >  include/linux/power/bq24261_charger.h              |   27 +
> >  5 files changed, 1279 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/power/bq24261.txt
> >  create mode 100644 drivers/power/bq24261_charger.c
> >  create mode 100644 include/linux/power/bq24261_charger.h
> >
> > diff --git a/Documentation/devicetree/bindings/power/bq24261.txt b/Documentation/devicetree/bindings/power/bq24261.txt
> > new file mode 100644
> > index 0000000..25fc5c4
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/power/bq24261.txt
> > @@ -0,0 +1,37 @@
> > +Binding for TI bq24261 Li-Ion Charger
> 
> Please split the bindings into separate patch (the first patch in patchset).
> 
> > +
> > +Required properties:
> > +- compatible: Should contain one of the following:
> > +    * "ti,bq24261"
> > +- reg: integer, i2c address of the device.
> > +- ti,charge-current: integer, default charging current (in mA);
> > +- ti,charge-voltage: integer, default charging voltage (in mV);
> > +- ti,termination-current: integer, charge will be terminated when current in
> > +    constant-voltage phase drops below this value (in mA);
> > +- ti,max-charge-current: integer, maximum charging current (in mA);
> > +- ti,max-charge-voltage: integer, maximum charging voltage (in mV);
> > +- ti,min-charge-temperature: integer, minimum charging temperature (in DegC);
> > +- ti,max-charge-temperature: integer, maximum charging temperature (in DegC).
> 
> Before accepting "[PATCH 13/13] dt: power: bq24257-charger: Cover
> additional devices"
> http://www.spinics.net/lists/devicetree/msg92134.html
> 
> could you and Andreas figure out common bindings? Look at this:
> 
> +- ti,charge-current: integer, maximum charging current in uA.
> +- ti,charge-current: integer, default charging current (in mA);
> 
> Different meaning and different units. This is madness! :)
> 
> In the same time you are adding TI-common bindings (not device
> specific, there is no prefix) so I would expect exactly the same
> bindings if it is possible.

Krzysztof, good observation! In bq2425x_charger.c (formerly known as
bq24257_charger.c :) that I worked on the unit used was uA. At that time
I did a quick check and there didn't seem to be a clear standard whether
to use the "micro" or "milli" units - different drivers use different
units. However there seems to be a tendency for the TI drivers to prefer
"milli" (bq2415x_charger.c, bq24735-charger.c)

Personally I think "milli" units are more appropriate for chargers since
they provide sufficient granularity and the numbers don't become too big
(try typing a voltage in the Volt-range in uV, it's very easy to get the
number of 0s wrong). However since the driver was already there I left
that aspect alone to preserve compatibility.

> > +
> > +Optional properties:
> > +- ti,thermal-sensing: boolean, if present thermal regulation will be enabled;
> 
> What is the requirement for thermal-sensing? Can it be enabled always?
> If yes, then this is not really a hardware property.
> 
> > +- ti,enable-user-write: boolean, if present driver will allow the user space
> > +    to control the charging current and voltage through sysfs;
> 
> This is not DT property. It does not describe hardware.

I take responsibility for this one :) In an earlier thread we were
discussing that it will be better to prevent sysfs write access to
"dangerous" charger parameters (charge voltage, current, ...) but I
argued that such access might still be desirable during development and
debug, and that a DT property could be used to allow such write access
(with the default being the charger properties being made read-only) -
this way giving the best of both worlds. However then when I updated the
bq24157_charger.c driver I ended up not really needing and implementing
this feature.

Out of curiosity, if it against best-practice to expose non hardware
properties, how would one best address the above use case? Compile time
switch? A sysfs property that allows write-enabling the other sysfs
properties (doesn't sound right). Or...?

--
Andreas Dannenberg
Texas Instruments Inc

> Best regards,
> Krzysztof
> 
> > +
> > +Example:
> > +
> > +bq25890 {
> > +        compatible = "ti,bq24261
> > +        reg = <0x6b>;
> > +
> > +        ti,charge-current = <1000>;
> > +        ti,charge-voltage = <4200>;
> > +        ti,termination-current = <128>;
> > +        ti,max-charge-current = <3000>;
> > +        ti,max-charge-voltage = <4350>;
> > +        ti,min-charge-temperature = <0>;
> > +        ti,max-charge-temperature = <60>;
> > +
> > +        ti,thermal-sensing;
> > +        ti,enable-user-write;
> > +};
> > diff --git a/drivers/power/Kconfig b/drivers/power/Kconfig
> > index f8758d6..cd47d0d 100644
> > --- a/drivers/power/Kconfig
> > +++ b/drivers/power/Kconfig
> > @@ -396,6 +396,12 @@ config CHARGER_BQ24190
> >         help
> >           Say Y to enable support for the TI BQ24190 battery charger.
> >
> > +config CHARGER_BQ24261
> > +       tristate "TI BQ24261 charger driver"
> > +       depends on I2C && EXTCON
> > +       help
> > +         Say Y here to enable support for TI BQ24261 battery charger.
> > +
> >  config CHARGER_BQ24257
> >         tristate "TI BQ24257 battery charger driver"
> >         depends on I2C
> > diff --git a/drivers/power/Makefile b/drivers/power/Makefile
> > index 5752ce8..bec8409 100644
> > --- a/drivers/power/Makefile
> > +++ b/drivers/power/Makefile
> > @@ -59,6 +59,7 @@ obj-$(CONFIG_CHARGER_MAX8997) += max8997_charger.o
> >  obj-$(CONFIG_CHARGER_MAX8998)  += max8998_charger.o
> >  obj-$(CONFIG_CHARGER_BQ2415X)  += bq2415x_charger.o
> >  obj-$(CONFIG_CHARGER_BQ24190)  += bq24190_charger.o
> > +obj-$(CONFIG_CHARGER_BQ24261)  += bq24261_charger.o
> >  obj-$(CONFIG_CHARGER_BQ24257)  += bq24257_charger.o
> >  obj-$(CONFIG_CHARGER_BQ24735)  += bq24735-charger.o
> >  obj-$(CONFIG_CHARGER_BQ25890)  += bq25890_charger.o
--
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