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

[Matti Vaittinen]

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@xxxxxxxxx>
> > Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> >
> > ---
> > 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@xxxxxxxxxx/


Yours,
	-- Matti