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

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Message-ID: <20389a09-1c69-40fa-a937-289a104d57fa@gmail.com>
Date: Mon, 8 Dec 2025 09:47:43 +0200
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Andreas Kemnade <andreas@...nade.info>, lee@...nel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mfd: bd71828: Add some missing charger related registers

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 have something in preparation for the power supply driver, but I am
> sending this now if this might go in earlier e.g. via  BD72720
> immutable branch to avoid more immutable branches.
> @Matti: Can you check the situation with the other chips supported
> by that driver. Is that register there, too?

Sure.

Just purely based on the data-sheets:

- BD71815: I didn't find one.
- BD71879: (As you know) - basically the same as BD71828, so they can
   both use the BD71828_REG_ILIM_STAT and BD71828_REG_DCIN_SET.
- BD72720:
   1: I see 'CHG_ILIM_STAT' with ILIM_VBUS_STAT[6:0], which says:
	"Actual value of VBUS current-limitation. The VBUS current limit
	is increased or decreased automatically. The actual limit can be
	read from ILIM_VBUS_STAT register."
	This may, or may not be related to the stuff you are working
	with. I think I have this register included in the
	include/linux/mfd/rohm-bd72720.h. On top of that, the BD72720
	has OTP options to configure (time) "Interval for VBUS Current
	Limitation / Relaxation".
   2: I see a read-only 'CHG_VBUS_STAT' with 'ILIM_VBUS' bit and:
	"0 = Normal operation
	1 = Automatic limit control"
   3: I see enable/disable control for:
	"VBUS input current limit in Battery Assist"
   4: There is also: CHG_VBUS_SET with IBUS_INLIM[6:0], which says:
	"VBUS current limit setting for Charge. VBUS current limit is
	automatically changed to supply enough current to the Battery
	Charger. Present current limit is available to read from
	ILIM_VBUS_STAT register." This may be something similar to the
	DCIN_SET.

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?

Yours,
	-- Matti


---
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~