linux-kernel - Re: [PATCH v5 04/16] dt-bindings: battery: Voltage drop properties

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Message-ID: <176365507949.1467967.14779548559679744817.robh@kernel.org>
Date: Thu, 20 Nov 2025 10:11:19 -0600
From: "Rob Herring (Arm)" <robh@...nel.org>
To: Matti Vaittinen <matti.vaittinen@...ux.dev>
Cc: Pavel Machek <pavel@...nel.org>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	devicetree@...r.kernel.org, Liam Girdwood <lgirdwood@...il.com>,
	Sebastian Reichel <sre@...nel.org>, Mark Brown <broonie@...nel.org>,
	linux-gpio@...r.kernel.org, Andreas Kemnade <andreas@...nade.info>,
	Michael Turquette <mturquette@...libre.com>,
	linux-pm@...r.kernel.org, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	linux-kernel@...r.kernel.org, Stephen Boyd <sboyd@...nel.org>,
	Matti Vaittinen <mazziesaccount@...il.com>,
	linux-clk@...r.kernel.org, Conor Dooley <conor+dt@...nel.org>,
	Lee Jones <lee@...nel.org>, linux-rtc@...r.kernel.org,
	linux-leds@...r.kernel.org,
	Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
	Bartosz Golaszewski <brgl@...ev.pl>
Subject: Re: [PATCH v5 04/16] dt-bindings: battery: Voltage drop properties


On Thu, 20 Nov 2025 10:20:24 +0200, Matti Vaittinen wrote:
> From: Matti Vaittinen <mazziesaccount@...il.com>
> 
> 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" (voltage drop rate) 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
> BD71815, BD71828, BD72720 and some other ROHM chargers. (Note, charger
> drivers aren't upstream yet).
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> 
> ---
> 
> Revision history:
>  v4 => v5:
>  - Move volt-drop parameters from rohm,vdr-battry,yaml to the
>    battery.yaml
>  - drop rohm, -prefix from volt-drop-* properties
>  - Drop the rohm,vdr-battry,yaml
>  - Add comment clarifying what the rohm,volt-drop-* properties are for
>    because this may no longer be obvious as they were moved to common
>    battery.yaml
>  - Drop Linus Walleij's rb-tag because the concept was changed
> 
>  v3 => v4:
>  - No changes
> 
>  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". There were some discussion whether these
> properties should be in their own file, or if they should be added to
> battery.yaml. Discussion can be found from:
> https://lore.kernel.org/all/52b99bf7-bfea-4cee-aa57-4c13e87eaa0d@gmail.com/
> This patch implements the volt-drop properties as generic (not vemdor
> specific) properties in the battery.yaml. It's worth noting that these
> properties 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, like Kobo e-readers though.
> ---
>  .../bindings/power/supply/battery.yaml        | 22 +++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 

Reviewed-by: Rob Herring (Arm) <robh@...nel.org>