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Subject: Re: [PATCH v3 2/4] mfd: max77620: add documentation for backup
 battery charging
From:   Mark Zhang <markz@nvidia.com>
To:     Rob Herring <robh+dt@kernel.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>
CC:     Lee Jones <lee.jones@linaro.org>,
        Mark Rutland <mark.rutland@arm.com>,
        <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        <linux-tegra@vger.kernel.org>
References: <20190212064353.7451-1-markz@nvidia.com>
 <20190212064353.7451-3-markz@nvidia.com>
 <CAL_JsqKiL8A+SBwqLzYa9djWBT1S+2kxUUB4iuKWX7EoqXouCw@mail.gmail.com>
 <91d3d8f8-0b96-c442-5674-3eff8209848b@nvidia.com>
Message-ID: <b808a706-19d0-4cae-8c99-2163a64d7884@nvidia.com>
Date:   Tue, 19 Feb 2019 10:09:40 +0800
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On 2/19/2019 10:07 AM, Mark Zhang wrote:
> On 2/19/2019 2:06 AM, Rob Herring wrote:
>> On Tue, Feb 12, 2019 at 12:44 AM Mark Zhang <markz@nvidia.com> wrote:
>>>
>>> Adding documentation for 3 new backup battery charging dts
>>> properties:
>>> - maxim,charging-current-microamp
>>> - maxim,charging-voltage-microvolt
>>> - maxim,output-resister-ohms
>>
>> What's the difference between the 77620 and 77650 as there's patches
>> on the list for the 77650 too. The properties are similar, but seems
>> to be main vs. backup battery charger. We should have common
>> properties for this.
> 
> Rob, it's different. The RTC in max77620 is supplied from a backup
> battery and consumes 2.0uA (IBBATT) when no other power sources are
> available. So unlike max77620 battery charging, which provides features

Oops... s/unlike max77620/unlike max77650.

Mark

> like:
> 
> static enum power_supply_property max77650_charger_properties[] = {
> 	POWER_SUPPLY_PROP_STATUS,
> 	POWER_SUPPLY_PROP_ONLINE,
> 	POWER_SUPPLY_PROP_CHARGE_TYPE
> };
> 
> For backup battery charging in max77620, what we can do is just setting
> those 3 parameters. We don't know whether it's charging, whether the
> backup battery is online, the percentage of the charging progress, and
> etc. That's why I mentioned before that it's not appropriate to create
> it as a power supply driver.
> 
> Mark
> 
>>
>>> Signed-off-by: Mark Zhang <markz@nvidia.com>
>>> ---
>>>  .../devicetree/bindings/mfd/max77620.txt      | 20 +++++++++++++++++++
>>>  1 file changed, 20 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/mfd/max77620.txt b/Documentation/devicetree/bindings/mfd/max77620.txt
>>> index 9c16d51cc15b..88825eaf2567 100644
>>> --- a/Documentation/devicetree/bindings/mfd/max77620.txt
>>> +++ b/Documentation/devicetree/bindings/mfd/max77620.txt
>>> @@ -122,6 +122,26 @@ For DT binding details of different sub modules like GPIO, pincontrol,
>>>  regulator, power, please refer respective device-tree binding document
>>>  under their respective sub-system directories.
>>>
>>> +Backup Battery:
>>> +==============
>>> +This sub-node configure charging backup battery of the device. Device has
>>> +support of charging the backup battery. The subnode name is "backup-battery".
>>> +The property for backup-battery child nodes as:
>>> +Presence of this child node will enable the backup battery charging.
>>> +
>>> +Optional properties:
>>> +       -maxim,charging-current-microamp: Charging current setting.
>>> +                       The device supports 50/100/200/400/600/800uA.
>>> +                       If this property is unavailable then it will
>>> +                       charge with 50uA.
>>> +       -maxim,charging-voltage-microvolt: Charging Voltage Limit Setting.
>>> +                       Device supports 2500000/3000000/3300000/350000uV.
>>> +                       Default will be set to 2500mV. The voltage will be roundoff
>>> +                       to nearest lower side if other than above is configured.
>>> +       -maxim,output-resister-ohms: Output resistor on Ohm.
>>> +                       Device supports 100/1000/3000/6000 Ohms.
>>> +                       Default will be set to 1000 Ohm.
>>> +
>>>  Example:
>>>  --------
>>>  #include <dt-bindings/mfd/max77620.h>
>>> --
>>> 2.19.2
>>>