linux-kernel - Re: [PATCH 17/22] power: supply: add battery driver for AXP20X and AXP22X PMICs

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Date:   Fri, 6 Jan 2017 09:29:07 +0100
From:   Quentin Schulz <quentin.schulz@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Jonathan Cameron <jic23@...nel.org>, knaack.h@....de,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sebastian Reichel <sre@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Lee Jones <lee.jones@...aro.org>, linux-iio@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Icenowy Zheng <icenowy@...c.xyz>,
        Bruno Prémont <bonbons@...ux-vserver.org>
Subject: Re: [PATCH 17/22] power: supply: add battery driver for AXP20X and
 AXP22X PMICs

Hi,

On 06/01/2017 04:39, Chen-Yu Tsai wrote:
>  Hi,
> 
> On Tue, Jan 3, 2017 at 12:37 AM, Quentin Schulz
> <quentin.schulz@...e-electrons.com> wrote:
[...]
>> +       case POWER_SUPPLY_PROP_CURRENT_MAX:
>> +               ret = regmap_read(axp20x_batt->regmap, AXP20X_CHRG_CTRL1, &reg);
>> +               if (ret)
>> +                       return ret;
>> +
>> +               reg &= AXP20X_CHRG_CTRL1_TGT_CURR;
>> +               val->intval = reg * 100000 + 300000;
>> +               break;
> 
> 
> This controls the charge current. I believe the correct property to use
> is CONSTANT_CHARGE_CURRENT. And you should add CONSTANT_CHARGE_CURRENT_MAX
> which returns the highest possible setting.
> 

ACK.

> Also letting the user control this might not always be a good idea.
> IIUC, LiPo batteries can only be charged at 1C, where C is the
> rated capacity (X mAh).
> 

OK. Should I get the charge current from a DT property then?

Like "x-powers,charge-current = <300000>;"
It's close to what has been done in bq24257_charger for example.

[...]
>> +static enum power_supply_property axp20x_battery_props[] = {
>> +       POWER_SUPPLY_PROP_PRESENT,
>> +       POWER_SUPPLY_PROP_ONLINE,
>> +       POWER_SUPPLY_PROP_STATUS,
>> +       POWER_SUPPLY_PROP_VOLTAGE_NOW,
>> +       POWER_SUPPLY_PROP_CURRENT_NOW,
>> +       POWER_SUPPLY_PROP_CURRENT_MAX,
>> +       POWER_SUPPLY_PROP_HEALTH,
>> +       POWER_SUPPLY_PROP_VOLTAGE_MAX_DESIGN,
>> +       POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
>> +       POWER_SUPPLY_PROP_CAPACITY,
> 
> You can also add POWER_SUPPLY_PROP_TECHNOLOGY, which would return
> POWER_SUPPLY_TECHNOLOGY_LIPO.
> 

Hum.. There are also POWER_SUPPLY_TECHNOLOGY_LION,
POWER_SUPPLY_TECHNOLOGY_LiFe and POWER_SUPPLY_TECHNOLOGY_LiMn which are
all Lithium-based batteries. From the datasheet, it can take a "single
cell Li-battery (Li-Ion/Polymer)". So I guess it's either
POWER_SUPPLY_TECHNOLOGY_LION or POWER_SUPPLY_TECHNOLOGY_LIPO.

> It is also possible to do POWER_SUPPLY_PROP_CHARGE_TYPE. According
> to the manual, if the battery is charging, it is in constant current
> mode (POWER_SUPPLY_CHARGE_TYPE_FAST) when V_battery < V_target.
> When V_battery == V_target, it is in constant voltage mode, though
> I don't think this is the same as POWER_SUPPLY_CHARGE_TYPE_TRICKLE.
> When it is not charging, you can return POWER_SUPPLY_CHARGE_TYPE_NONE.
> 

ACK, I'll look into that.

Thanks,
Quentin

-- 
Quentin Schulz, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com