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Subject: Re: [PATCH v2 0/4] Add max77620 charging & low battery support
To:     Lee Jones <lee.jones@linaro.org>
CC:     <blaws05@gmail.com>, <robh+dt@kernel.org>, <mark.rutland@arm.com>,
        <devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-tegra@vger.kernel.org>
References: <20190129085531.32364-1-markz@nvidia.com>
 <20190207084836.GF4672@dell>
 <a43eb007-c984-a209-2b4e-6672807029aa@nvidia.com>
 <20190212080457.GL20638@dell>
From:   Mark Zhang <markz@nvidia.com>
Message-ID: <4d0a1e3c-becd-70a8-920f-a37ee1ee48cc@nvidia.com>
Date:   Tue, 12 Feb 2019 16:29:51 +0800
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On 2/12/2019 4:04 PM, Lee Jones wrote:
> On Tue, 12 Feb 2019, Mark Zhang wrote:
> 
>> On 2/7/2019 4:48 PM, Lee Jones wrote:
>>> On Tue, 29 Jan 2019, Mark Zhang wrote:
>>>
>>>> This patch set adds support for max77620 backup battery charging and
>>>> low battery monitoring.
>>>>
>>>> Changes in v2:
>>>> - Add devicetree binding documentation
>>>>
>>>> Mark Zhang (4):
>>>>   mfd: max77620: Add backup battery charger support
>>>>   mfd: max77620: add documentation for backup battery charging
>>>>   mfd: max77620: Add low battery monitor support
>>>>   mfd: max77620: add documentation for low battery monitoring
>>>>
>>>>  .../devicetree/bindings/mfd/max77620.txt      |  34 +++++
>>>>  drivers/mfd/max77620.c                        | 137 +++++++++++++++++-
>>>
>>> All of this needs moving out to the correct subsystem.
>>>
>>> drivers/power/supply/max77620-battery.c looks right.
>>
>> Actually max77620 is not a power supply device. This patch set adds 2
>> features:
>> - Backup battery charger. The RTC in max77620 is supplied from a backup
>> battery and consumes 2.0uA when no other power sources are available. So
>> basically this is not a system battery charger, it's just for RTC.
>> - Low battery monitoring. This is for monitoring the system main battery
>> voltage, so max77620 can shutdown or reset the SoC accordingly. But I
>> think this doesn't conform the idea of "power supply" driver as well.
> 
> Most other battery handling seems to happen in
> drivers/power/supply/*.battery*.  If that's not the right location,
> then you need to find a place for it to go.  MFDs do not provide
> useful functionality per say - that is the role of the child devices.
> 

Understood. Looking at "enum power_supply_property", battery handling
drivers are able to get battery capacity/current
voltage/temperature/status/... and etc, which is making sense. But my
patch set doesn't do this kind of things at all so I think the power
supply framework doesn't fit here. Let me check other similar device
drivers... hope to get inspired. Thanks Lee.

Mark