linux-kernel - Re: [PATCH v2 02/15] dt-bindings: Add trickle-charge upper limit

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Message-ID: <a81fba66-adf0-440f-96e1-bf3a83d504d8@gmail.com>
Date: Wed, 29 Oct 2025 08:22:45 +0200
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
 Lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Sebastian Reichel <sre@...nel.org>,
 Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Linus Walleij <linus.walleij@...aro.org>,
 Bartosz Golaszewski <brgl@...ev.pl>, Andreas Kemnade <andreas@...nade.info>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>,
 linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-clk@...r.kernel.org, linux-gpio@...r.kernel.org,
 linux-rtc@...r.kernel.org
Subject: Re: [PATCH v2 02/15] dt-bindings: Add trickle-charge upper limit

On 29/10/2025 08:03, Krzysztof Kozlowski wrote:
> On Mon, Oct 27, 2025 at 01:45:05PM +0200, Matti Vaittinen wrote:
>> Some of the chargers for lithium-ion batteries use a trickle-charging as
>> a first charging phase for very empty batteries, to "wake-up" the battery.
> 
> In the few cases I was dealing with charging circuits, trickle charging
> was used in context of top-off charging, so when battery is 100%. It's
> also documented at Wiki like that:
> https://en.wikipedia.org/wiki/Trickle_charging
> 
>> Trickle-charging is a low current, constant current phase. After the
>> voltage of the very empty battery has reached an upper limit for
>> trickle charging, the pre-charge phase is started with a higher current.
>>
>> Allow defining the upper limit for trickle charging voltage, after which
>> the charging should be changed to the pre-charging.


> pre-charging is the trickle charging, no? Or you want to say that
> trickle-charging is pre-pre-charging? But then what is pre-charging in
> this binding?

There are the (usual?) pre-charging and fast-charging phases in the Rohm 
devices. Furthermore, the fast-charging is divided to constant current 
and constant voltage phases.

In addition to this, there is a 'trickle-charging' -phase for a very 
empty battery. This is already reflected by existing bindings:
trickle-charge-current-microamp, Please, see:
bbcecd1b9335 ("dt-bindings: Add trickle-charge upper limit")

I also did do some ASCII art for my very first charger driver binding:
https://elixir.bootlin.com/linux/v6.18-rc1/source/Documentation/devicetree/bindings/power/supply/rohm,bd99954.yaml

Do you think a comment linking to this drawing would help?

> 
>>
>> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
>> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
>>
>> ---
>> Revision history:
>>   RFCv1 =>:
>>   - No changes
>> ---
>>   Documentation/devicetree/bindings/power/supply/battery.yaml | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/power/supply/battery.yaml b/Documentation/devicetree/bindings/power/supply/battery.yaml
>> index 491488e7b970..66bed24b3dee 100644
>> --- a/Documentation/devicetree/bindings/power/supply/battery.yaml
>> +++ b/Documentation/devicetree/bindings/power/supply/battery.yaml
>> @@ -66,6 +66,9 @@ properties:
>>     trickle-charge-current-microamp:
>>       description: current for trickle-charge phase
>>   
>> +  tricklecharge-upper-limit-microvolt:
> 
> Please keep existing format, look three lines above. trickle-charge-....
> 
> But I believe this is wrong. Trickle charging does not switch to
> anything more, there is no fast charging after trickle. You have some
> sort of pre-pre-charging, which is just pre-charging.

There is trickle, pre and fast-charge phases. Furthermore, the 
fast-charge is further divided to CC and CV. Finally, if my memory 
serves me well, Linus W did explain me that some chargers use 
'trickle-charging' as a _last_ charging phase for a full battery. Thus 
the term 'trickle-charging' is slightly confusing - but it is already 
used by the existing bindings...

https://lore.kernel.org/all/20211116001755.2132036-1-linus.walleij@linaro.org/


Yours,
	-- Matti