linux-kernel - Re: [PATCH v3 04/16] dt-bindings: power: supply: BD72720 managed battery

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Message-Id: <176233321101.143066.16817673032324313304.robh@kernel.org>
Date: Wed, 05 Nov 2025 03:00:14 -0600
From: "Rob Herring (Arm)" <robh@...nel.org>
To: Matti Vaittinen <matti.vaittinen@...ux.dev>
Cc: Linus Walleij <linus.walleij@...aro.org>, 
 Alexandre Belloni <alexandre.belloni@...tlin.com>, 
 linux-rtc@...r.kernel.org, Stephen Boyd <sboyd@...nel.org>, 
 Matti Vaittinen <matti.vaittinen@...rohmeurope.com>, 
 Liam Girdwood <lgirdwood@...il.com>, linux-pm@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Bartosz Golaszewski <brgl@...ev.pl>, 
 Pavel Machek <pavel@...nel.org>, linux-leds@...r.kernel.org, 
 Sebastian Reichel <sre@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
 Michael Turquette <mturquette@...libre.com>, devicetree@...r.kernel.org, 
 linux-gpio@...r.kernel.org, Matti Vaittinen <mazziesaccount@...il.com>, 
 Mark Brown <broonie@...nel.org>, Andreas Kemnade <andreas@...nade.info>, 
 Lee Jones <lee@...nel.org>, linux-clk@...r.kernel.org, 
 Krzysztof Kozlowski <krzk+dt@...nel.org>
Subject: Re: [PATCH v3 04/16] dt-bindings: power: supply: BD72720 managed
 battery


On Wed, 05 Nov 2025 09:36:49 +0200, Matti Vaittinen wrote:
> From: Matti Vaittinen <mazziesaccount@...il.com>
> 
> 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@...il.com>
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> 
> ---
> NOTE:
> Linus' rb-tag holds only if there's no further comments from Rob.
> 
> Revision history:
>  v2 => v3:
>  - Constrain VDR threshold voltage to 48V
>  - Use standard '-bp' -suffix for the rohm,volt-drop-soc
> 
>  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
> 

My bot found errors running 'make dt_binding_check' on your patch:

yamllint warnings/errors:

dtschema/dtc warnings/errors:
/builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/power/supply/rohm,vdr-battery.example.dtb: battery (simple-battery): 'degrade-cycle-microamp-hours', 'rohm,volt-drop-0-microvolt', 'rohm,volt-drop-1-microvolt', 'rohm,volt-drop-2-microvolt', 'rohm,volt-drop-3-temp-microvolt', 'rohm,volt-drop-soc-bp', 'rohm,volt-drop-temperatures-millicelsius', 'rohm,voltage-vdr-thresh-microvolt' do not match any of the regexes: '^ocv-capacity-table-[0-9]+$', '^pinctrl-[0-9]+$'
	from schema $id: http://devicetree.org/schemas/power/supply/battery.yaml

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/a45e7230ecd08eed2081cbe7e7b4719d1fc8a581.1762327887.git.mazziesaccount@gmail.com

The base for the series is generally the latest rc1. A different dependency
should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note
that DT_SCHEMA_FILES can be set to your schema file to speed up checking
your schema. However, it must be unset to test all examples with your schema.