linux-kernel - Re: [PATCH V4] drivers/rtc/rtc-palmas.c: support for backup battery charging

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Date:	Thu, 8 Aug 2013 00:16:11 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Mark Rutland <mark.rutland@....com>
CC:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"rob@...dley.net" <rob@...dley.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	"gg@...mlogic.co.uk" <gg@...mlogic.co.uk>,
	"kishon@...com" <kishon@...com>,
	Stephen Warren <swarren@...dia.com>,
	Pawel Moll <Pawel.Moll@....com>,
	"ian.campbell@...rix.com" <ian.campbell@...rix.com>,
	"broonie@...nel.org" <broonie@...nel.org>
Subject: Re: [PATCH V4] drivers/rtc/rtc-palmas.c: support for backup battery
 charging

On Wednesday 07 August 2013 10:08 PM, Mark Rutland wrote:
> On Wed, Aug 07, 2013 at 11:29:52AM +0100, Laxman Dewangan wrote:
>> +Optional properties:
>> +- ti,back-battery-charge-enable: The Palmas series device like TPS65913 or
>> +	TPS80036 supports the battery backup for powering the RTC when main
>> +	battery is removed or in very low power state. This flag will enable
>> +	the backup battery charging.
> I don't like the wording here as it implies that an OS *must* charge the
> device, rather than that it *can* charge the device. How about:
>
>   - ti,backup-battery-chargeable: There is a chargeable backup battery
>                                   present.
>

The *org* property tells whether charging should be enable or not. This 
is enabled during init and it is not the runtime configuration for 
enable/disable.
By saying "backup-battery-chargeable" means it need other 
interface/calls to start charging. It does not reflect that charging 
will be enabled by default.



>> +- ti,back-battery-charge-low-current: Configure lower charging current. Device
>> +	supports the charging current as < 100mA or >100mA. Low current will
>> +	set as <100mA.
> This is somewhat unclear as it reads as a runtime configuration choice,
> rather than some instances of the device only support being changed at
> low currents (as I assume is the case?). How about:
>
>    - ti,backup-battery-low-current: The backup battery is only chargeable
>                                     at currents below 100mA.

Hmm.. I think even if battery can be charge for more than 100mA, there 
is choice of configure it for less than 100mA.

> What happens if we charge at the wrong current?
Not much sure but I think it can create battery damage.


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