Re: [PATCH v2 03/15] dt-bindings: power: supply: BD72720 managed battery

[Rob Herring <robh@kernel.org>]

On Mon, Oct 27, 2025 at 01:45:23PM +0200, Matti Vaittinen wrote:
> The BD72720 PMIC has a battery charger + coulomb counter block. These
> can be used to manage charging of a lithium-ion battery and to do fuel
> gauging.
> 
> ROHM has developed a so called "zero-correction" -algorithm to improve
> the fuel-gauging accuracy close to the point where battery is depleted.
> This relies on battery specific "VDR" tables, which are measured from
> the battery, and which describe the voltage drop rate. More thorough
> explanation about the "zero correction" and "VDR" parameters is here:
> https://lore.kernel.org/all/676253b9-ff69-7891-1f26-a8b5bb5a421b@fi.rohmeurope.com/
> 
> Document the VDR zero-correction specific battery properties used by the
> BD72720 and some other ROHM chargers.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
> ---
> Revision history:
>  RFCv1 => v2:
>  - Add units to rohm,volt-drop-soc (tenths of %)
>  - Give real temperatures matching the VDR tables, instead of vague
>    'high', 'normal', 'low', 'very low'. (Add table of temperatures and
>    use number matching the right temperature index in the VDR table name).
>  - Fix typoed 'algorithm' in commit message.
> 
> The parameters are describing the battery voltage drop rates - so they
> are properties of the battery, not the charger. Thus they do not belong
> in the charger node.
> 
> The right place for them is the battery node, which is described by the
> generic "battery.yaml". I was not comfortable with adding these
> properties to the generic battery.yaml because they are:
>   - Meaningful only for those charger drivers which have the VDR
>     algorithm implemented. (And even though the algorithm is not charger
>     specific, AFAICS, it is currently only used by some ROHM PMIC
>     drivers).
>   - Technique of measuring the VDR tables for a battery is not widely
>     known. AFAICS, only folks at ROHM are measuring those for some
>     customer products. We do have those tables available for some of the
>     products though (Kobo?).
> ---
>  .../power/supply/rohm,vdr-battery.yaml        | 80 +++++++++++++++++++
>  1 file changed, 80 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/power/supply/rohm,vdr-battery.yaml
> 
> diff --git a/Documentation/devicetree/bindings/power/supply/rohm,vdr-battery.yaml b/Documentation/devicetree/bindings/power/supply/rohm,vdr-battery.yaml
> new file mode 100644
> index 000000000000..1ab3418d4338
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/power/supply/rohm,vdr-battery.yaml
> @@ -0,0 +1,80 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/power/supply/rohm,vdr-battery.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Battery managed by the BD72720 PMIC
> +
> +maintainers:
> +  - Matti Vaittinen <mazziesaccount@gmail.com>
> +
> +description:
> +  A battery which has VDR parameters measuerd for ROHM chargers.
> +
> +allOf:
> +  - $ref: battery.yaml#
> +
> +properties:
> +  rohm,voltage-vdr-thresh-microvolt:
> +    description: Threshold for starting the VDR correction

No constraints? Is 4000V okay?

> +
> +  rohm,volt-drop-soc:
> +    description: Table of capacity values matching the values in VDR tables.
> +      The value should be given as tenths of a percentage.

We have a standard unit for this too. '-bp' or basis points (1/100 of 
percent).

> +    $ref: /schemas/types.yaml#/definitions/uint32-array
> +
> +  rohm,volt-drop-temperatures-millicelsius:
> +    description: An array containing the temperature in milli celsius, for each
> +      of the VDR lookup table.
> +
> +patternProperties:
> +  '^rohm,volt-drop-[0-9]-microvolt':
> +    description: Table of the voltage drop rate (VDR) values. Each entry in the
> +      table should match a capacity value in the rohm,volt-drop-soc table.
> +      Furthermore, the values should be obtained for the temperature given in
> +      rohm,volt-drop-temperatures-millicelsius table at index matching the
> +      number in this table's name.
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    power {
> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +
> +      battery: battery {
> +        compatible = "simple-battery";
> +
> +        ocv-capacity-celsius = <25>;
> +        ocv-capacity-table-0 = <4200000 100 4184314 100 4140723 95 4099487 90
> +          4060656 85 4024350 80 3991121 75 3954379 70 3913265 65 3877821 60
> +          3855577 55 3837466 50 3822194 45 3809012 40 3795984 35 3780647 30
> +          3760505 25 3741532 20 3718837 15 3696698 10 3690594 5 3581427 0>;
> +
> +        rohm,volt-drop-soc = <1000 1000 950 900 850 800 750 700 650 600 550 500
> +          450 400 350 300 250 200 150 100 50 00 (-50)>;
> +
> +        rohm,volt-drop-temperatures-millicelsius = <45000 25000 5000 0>;
> +
> +        rohm,volt-drop-0-microvolt =  <100 100 102 104 106 109 114 124
> +          117 107 107 109 112 116 117 108 109 109 108 109 122 126 130>;
> +
> +        rohm,volt-drop-1-microvolt = <100 100 102 105 98 100 105 102
> +          101 99 98 100 103 105 109 117 111 109 110 114 128 141 154>;
> +
> +        rohm,volt-drop-2-microvolt = <100 100 98 107 112 114 118 118 112
> +          108 108 110 111 113 117 123 131 144 157 181 220 283 399>;
> +
> +        rohm,volt-drop-3-temp-microvolt = <86 86 105 109 114 110 115 115
> +          110 108 110 112 114 118 124 134 136 160 177 201 241 322 403>;
> +
> +        rohm,voltage-vdr-thresh-microvolt = <4150000>;
> +
> +        charge-full-design-microamp-hours = <1799000>;
> +        voltage-max-design-microvolt = <4200000>;
> +        voltage-min-design-microvolt = <3500000>;
> +        degrade-cycle-microamp-hours = <131>;
> +      };
> +    };
> -- 
> 2.51.0
>