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

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Message-ID: <b81502cc-d91d-4801-ad72-034c20b1c72a@kernel.org>
Date: Wed, 29 Oct 2025 14:33:39 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Linus Walleij <linus.walleij@...aro.org>,
 Matti Vaittinen <mazziesaccount@...il.com>
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>, 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 14:26, Linus Walleij wrote:
> On Wed, Oct 29, 2025 at 7:22 AM Matti Vaittinen
> <mazziesaccount@...il.com> wrote:
> 
>>> 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/
> 
> I think we need to refer to a textbook or IEEE articles to get this
> terminology right.
> 
> As you say it appears "trickle-charging" is ambiguous.
> 
> Maybe what Krzysztof suggest to use: "pre-pre-charging" or
> "empty-battery-charging" or something like this is needed.
> 
> But we really need a trustworthy academic source here.

Trickle charging is accurate for both cases - pre-pre and top-off -
because it just describes very small current. That's why I found it in
many TI datasheets - mostly for Li-Ion batteries describing Matti's
case, but also in at least one case for Ni-Mh describing top-off (or
maintenance).

I am fine with the naming, but I want to be clear that this property
will describe trickle only in case of pre-pre charging. Termination
voltage simply does not fit the top-off/maintenance mode.

Best regards,
Krzysztof