On Tue, Sep 15, 2015 at 04:56:52PM +0900, Krzysztof Kozlowski wrote:

On 14.09.2015 22:54, Andreas Dannenberg wrote:

quoted

On Mon, Sep 14, 2015 at 03:11:32PM +0900, Krzysztof Kozlowski wrote:

quoted

On 12.09.2015 05:26, Andreas Dannenberg wrote:

quoted

Extend the bq24257 charger's device tree documentation to cover the
bq24250 and bq24251 devices as well feature additions.

Signed-off-by: Andreas Dannenberg <redacted>
---
 .../devicetree/bindings/power/bq24257.txt          | 59 ++++++++++++++++++++--
 1 file changed, 54 insertions(+), 5 deletions(-)

diff --git a/Documentation/devicetree/bindings/power/bq24257.txt b/Documentation/devicetree/bindings/power/bq24257.txt
index 5c9d394..4a88c96 100644
--- a/Documentation/devicetree/bindings/power/bq24257.txt
+++ b/Documentation/devicetree/bindings/power/bq24257.txt

@@ -1,21 +1,70 @@
-Binding for TI bq24257 Li-Ion Charger
+Binding for TI bq24250/bq24251/bq24257 Li-Ion Charger
 
 Required properties:
 - compatible: Should contain one of the following:
+ * "ti,bq24250"
+ * "ti,bq24251"
  * "ti,bq24257"
-- reg:			   integer, i2c address of the device.
+- reg: integer, i2c address of the device.
+- stat-gpios: GPIO used for the devices STAT_IN pin. Alternatively the pin can
+    also be defined through the standard interrupt definition properties (see
+    optional properties section below). Only use one method.
 - ti,battery-regulation-voltage: integer, maximum charging voltage in uV.
-- ti,charge-current:	   integer, maximum charging current in uA.
-- ti,termination-current:  integer, charge will be terminated when current in
-			   constant-voltage phase drops below this value (in uA).
+- ti,charge-current: integer, maximum charging current in uA.
+- ti,termination-current: integer, charge will be terminated when current in
+    constant-voltage phase drops below this value (in uA).
+
+Optional properties:
+- pg-gpios: GPIO used for connecting the bq2425x device PG (Power Good) pin.
+    This pin is not available on all devices however it should be used if
+    possible as this is the recommended way to obtain the charger's input PG
+    state. If this pin is not specified a software-based approach for PG
+    detection is used.
+- ti,current-limit: The maximum current to be drawn from the charger's input
+    (in uA). If this property is not specified a USB D+/D- signal based charger
+    type detection is used (if available) and the input limit current is set
+    accordingly. If the D+/D- based detection is not available on a given device
+    a default of 500,000 is used (=500mA).
+- ti,ovp-voltage: Configures the over voltage protection voltage (in uV). If
+    not specified a default of 6,5000,000 (=6.5V) is used.
+- ti,in-dpm-voltage: Configures the threshold input voltage for the dynamic
+    power path management (in uV). If not specified a default of 4,360,000
+    (=4.36V) is used.
+- ti,safety-timer-2x-enable: If this property is set to 1 the device's safety
+    timer is extended (slowed down) by a factor of two. Setting this property
+    to 0 or not providing it will leave the safety timer at its default
+    setting.

Now I spotted the difference in this binding from previous emails.
Previously you made it as a boolean property. Now it is a integer
property for a boolean value. It is unusual. If you expect a need (or a
possibility of need) of:
1. extending,
2. overriding,
3. using similar (extended) property in different drivers,
then it should be a real value, like:

1. ti,safety-timer: integer, in seconds

Hi Krzysztof,

I thought about this as well because the device actually allows
configuring different safety timer intervals (currently not exposed) and
it appears that the "2x enable" could be factored in there however it's
not as easy as it seems.  The "2x enable" is a dedicated HW feature
that's only being used in some states of the devices and with that does
not generally extend the safety timer under all conditions.

Right, I read also the datasheet which explains it.

quoted

quoted

2. ti,safety-timer-ratio/multiplier: integer, supported values are: 0
(use default) or 2 (slow down by factor of 2)

It is unusual and not obvious to use a integer value for boolean strict
property. With current solution you can actually only override it.

Yes that was the sole reason behind using integer instead of boolean.
The boolean "character" of this property was left intact because of the
direct mapping to a device HW feature (see below).

DT serves a purpose of providing information allowing the kernel to use
and configure the hardware. DT binding does not have to map device
property. In the same time having a device property does not mean you
create a DT binding.

If such requirement of mapping property to a HW feature was valid then
each driver would expose each register in DT. Sometimes platform data
did this... but DT is not pdata.
You're using such argument also below but this argument is not sufficient.

Sufficient argument would be: this property is necessary to configure
the hardware in different board configurations (so on different boards
it will have different values).

Example of device features not matching to DeviceTree:
 - configuration changing over time:
/sys/class/power/ds2760-battery.*/charge_full

 - various timers:
/sys/class/power_supply/max14577-charger/device/fast_charge_timer

 - various thresholds:
/sys/class/power_supply/max77693-charger/device/top_off_threshold_current

These are strictly HW features (they map to a bit in register) but they
are not related to configuring device for specific board. They serve for
user-space to use the devices in different ways.

In this case - the 2XTMR_EN - I assume that for certain batteries or
boards you want to extend the time of charging in case of special
conditions?

FWIW, I don't see any real benefit in manually changing the 2X timer at
all. The default setting is decent enough. The chip will automatically
switch to 2X timer in certain conditions: for example, when the
temperature threshold is exceeded and the charge current is
automatically lowered. This makes sense since it'll take the battery
more time to charge at a lower current.

It would probably make more sense to add a DT property to change the
'Safety Timer Time Limit' device property (which can be 0.75hrs, 6hrs,
9hrs or totally disabled) than the 2XTMR.

I omitted both when I originally added support for this chip since the
6hrs default safety timer seemed more than enough to charge a nowadays
battery, even at 500mA (provided by a standard USB port). But, future
batteries might (and probably will) have higher capacities and will take
longer to charge.

laurentiu