linux-kernel - Re: Implement devicetree support for AB8500 Btemp

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Date:	Fri, 14 Sep 2012 15:47:01 +0530
From:	Rajanikanth HV <rajanikanth.hv@...ricsson.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Rajanikanth HV <rajanikanth.hv@...aro.org>,
	Lee Jones <lee.jones@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus WALLEIJ <linus.walleij@...ricsson.com>,
	STEricsson_nomadik_linux <STEricsson_nomadik_linux@...t.st.com>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>
Subject: Re: Implement devicetree support for AB8500 Btemp



On Thursday 13 September 2012 08:07 PM, Arnd Bergmann wrote:
> On Thursday 13 September 2012, Rajanikanth HV wrote:
>> On Wednesday 12 September 2012 09:06 PM, Arnd Bergmann wrote:> > 
>>> If this is true, I don't understand what makes the 'supplied-to'
>>> properties you list in the device tree binding board specific. Are
>>> they not always done the same way? If so, you could just leave them
>>> out.
>> Precisely 'supplied-to' is not board specific, it was maintained as
>> platform_data which i migrated to dt-node. It is meant to establish
>> dependency across bm drivers based on power_supply property and
>> runtime battery attributes.
>> Basically, 'supplied-to' provides a way of exporting change in
>> power_supply_property and runtime batter characteristics so that other
>> bm devs shall make use or refer the updated values.
>> Ref: external_power_changed(...) call back api.
>> Note: all the bm drivers handles subset of power_supply property and
>>       battery attributes,
>>       ref: include/linux/power_supply.h and get_property(...) call back
>>       api across bm drivers.
> 
> Ok, so you want to just remove the property from the device tree,
> or do you want to establish a different method to specify these
> connections?
> 
>>> What does indeed seem to be needed is a place to identify the battery
>>> type, but it's not clear if the btemp device is the best place for
>>> that (maybe it is). 
>> I am not clear whether you are trying to correlate battery-type with
>> supplied-to. however, battery type is identified based on the
>> resistance value measured at batctrl pin which is expected to be in the
>> allowable limit of ab8500 device. This resistance limit varies across
>> battery types. This happens in btemp driver.
> 
> I wasn't correlating them. I just mentioned that unlike the supplied-to
> property, the battery type property does seem to belong into the device
> tree.
> 
>> For this, I would suggest you give a list of
>>> possible batteries and require a property such as
>>>
>>>  st-ericsson,battery-type: A string identifier for the type of battery,
>>> 			   which impacts how an operating system interpret
>>> 			   the sensor readings. Possible values include:
>>> 	* "none"	-- no battery connected
>>> 	* "li-ion-9100" -- Type 9100 Li-ION battery
>>> 	* <add any others that apply here>
>> Can do this, not precisely as "st-ericsson,battery-type", it will be as
>> battery-type = [unknown|NiMH|LION|...|]], reason being
>> allowable battery type is based on technology, as you can see the
>> possible types as:
>> POWER_SUPPLY_TECHNOLOGY_UNKNOWN = 0,
>>         POWER_SUPPLY_TECHNOLOGY_NiMH,
>>         POWER_SUPPLY_TECHNOLOGY_LION,
>>         POWER_SUPPLY_TECHNOLOGY_LIPO,
>>         POWER_SUPPLY_TECHNOLOGY_LiFe,
>>         POWER_SUPPLY_TECHNOLOGY_NiCd,
>>         POWER_SUPPLY_TECHNOLOGY_LiMn
>> Ref: include/linux/power_supply.h
>> Note: doing this will impact my of_probe(...), may slightly bloat the
>> code.
> 
> Ok.
> 
> If you want to make the battery type a generic property, it's probably
> best to start a separate binding document for this in
> Documentation/devicetree/bindings/power-supply/common.txt
> and document a string for each of these.
> 
> If we expect the property to be needed only for ab8500, please use
> a vendor prefix like 'stericsson,'.
it is fine to have battery-name in the battery-type property as said
above and to have binding document, the basic requirement is to
maintain the battery type information for a specified battery also
within the same technology of battery method, battery parameters may
vary. Presently battery-type and its dependent information is
maintained in the drivers/power/ folder as per the arnd review
sometimes back.




> 
> 	Arnd
> 
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