linux-kernel - Re: [PATCH] mfd: bd71828: Add some missing charger related registers

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Message-ID: <20251209102149.30c7ce19@kemnade.info>
Date: Tue, 9 Dec 2025 10:21:49 +0100
From: Andreas Kemnade <andreas@...nade.info>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: lee@...nel.org, linux-kernel@...r.kernel.org, sre@...nel.org
Subject: Re: [PATCH] mfd: bd71828: Add some missing charger related
 registers

On Mon, 8 Dec 2025 09:47:43 +0200
Matti Vaittinen <mazziesaccount@...il.com> wrote:

> On 07/12/2025 10:50, Andreas Kemnade wrote:
> > As there are some registers missing which are required for future charger
> > extensions, add them.
> > 
> > Signed-off-by: Andreas Kemnade <andreas@...nade.info>  
> 
> Reviewed-by: Matti Vaittinen <mazziesaccount@...il.com>
> 
> Thanks for working with this driver! Much appreciated :)
> 
[...]
> I asked for some clarification from the HQ folks - but they may be quite 
> busy, and my request(s) may not be at the top of the priority list. So, 
> let's see...
> 
> Are you planning to expose the current limit values to user-space? Allow 
> setting the control to AUTO/fixed value? I suppose this is what enabled 
> you to do some low-power charging, right?
> 
I am thinking about adding input_current_limit property and providing the
ILIM_DCIN_EN as a custom sysfs property like maybe "auto_input_current_limitation"

I had issues with using my bike hub dynamo and some solar panels
without any additional batteries in between, just  regulator (and
in the bike hub dynamo, of course a rectifier with a smoothing capacitor).
I would expect to just see the current limited so that voltage stays at the
anticollapse voltage, but that is not the case.
I have solved the problem with clearing ILIM_DCIN_EN and setting current
accordingly (often to something like 0.4A). I will try to use the next sun ray
arriving here to recheck. I have created a script to manipulate
things using i2cset in a lonely place in nature where I obviously
did not want to spend time with datasheets as short as possible.

The key point is not only low-power charging but also power sources with
changing properties.

Regards,
Andreas