On 14.09.2015 22:54, Andreas Dannenberg wrote:

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

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?

But I can certainly
change this to ti,safety-timer-multiplier and use 0/2. This avoids the
inaccuracy as explained above with just using ti,safety-timer (the
corresponding underlying device property should be separate and could be
exposed if ever needed) and still leaves room for this property to grow
which may come in handy later.

Hmmmm, the "2x" part of timer suggests to use a numerical value but
actually the datasheet does the opposite. I would not expect different
values... so your original idea makes sense (if DT is the place for it).
Overriding could be achieved with /delete-property/ (I forgot about it...).

quoted

Extending is possible but would look really weird, like:
	ti,safety-timer-2x-enable = <4>; /* Heh? 4x or (4*2)x ??? */

quoted

To add even more confusion: why this property has to be configured in
Device Tree? How it is related to the hardware? It rather looks like a
job for sysfs.

This property maps directly to a corresponding bit in the device
register map so yes it is related to the HW and IMHO should be
applicable to DT. The reason for not providing write access to that bit
via sysfs is the same as this driver doesn't have write access to other
"critical" properties such as charge current/voltages.

Responded to this above.

Best regards,
Krzysztof