Re: [RFC PATCH 06/13] mfd: bd71828: Support ROHM BD72720
From: Matti Vaittinen
Date: Wed Oct 15 2025 - 03:46:22 EST
On 14/10/2025 08:41, Matti Vaittinen wrote:
On 13/10/2025 16:19, Andreas Kemnade wrote:// snip
On Mon, 13 Oct 2025 12:27:33 +0300
Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
Hi Andreas!Well, you could also stack regmaps like ntxec.c is doing (but there
First of all, thanks for taking a look at this!
On 10/10/2025 16:03, Andreas Kemnade wrote:
On Fri, 10 Oct 2025 15:09:07 +0300
Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
+static int bd72720_get_secondary_regmap(struct i2c_client *i2c,
Does this 'secondary' have a specific purpose or a better name?
I am not entirely sure. When I asked this from the designers they just
told me that they needed more than 255 registers so they added another
slave address... (I'm not sure what would have been wrong with using a
page register). So, I assume they just placed stuff that didn't fit in
first 255 register there. But yeah, it looks like most of the registers
there are related to the charger. So, perhaps it isn't completely
misleading to use "charger regmap"? The data-sheet seems to be just
using "Register map 1" and "Register map 2" in the tables listing these
registers. I kind of like using something which maps easily to the
data-sheet, but I really have no strong opinion on this.
just another idea: What about one regmap with custom functions covering
both these adresses? Maybe that could even be added to the regmap
functionality, maybe with a 0x100 offset for the second range.
That way the rest of the code only needs to real with one regmap
and properly defined registers.
Interesting idea.
I suppose you mean something like implementing custom remap_read() and
regmap_write() - which would practically select the I2C adapter to use
based on the register address - and then doing same thing as the
regmap_i2c_smbus_i2c_write() / regmap_i2c_smbus_i2c_read() do?
I suppose this would mean duplicating the functionality provided by the
regmap_i2c_smbus_i2c_write() and the regmap_i2c_smbus_i2c_read(), which
are static. It'd also mean we'll lose the 1 to 1 mapping between the
register addresses in driver and addresses in the data-sheet. I agree
this wouldn't be such a huge thing if we used offset like 0x100 though.
for some very weird reason). That would avoid duplicating code.
If this works, then I kind of like this. It avoids using the platform data and simplifies the regmap getting in the power_supply driver. Thanks for the good idea Andreas!
Hmm. This morning I tested this approach. I converted the MFD driver and some sub-devices, and I mostly liked it. Mostly.
When adding the offset only to the addresses behind the 'secondary slave', the addresses behind the 'real slave' (which the MFD driver is bound), can be accessed using both the 'wrapper' and the 'real' regmap. Assuming the cache is kept in the 'real' regmaps. This is a small performance penalty compared to having the cache already in the wrapper, but it allows the drivers like the regulator driver, which only use the 'primary slave' to just get a regmap from the MFD parent, no matter whether they get the 'wrapper' of the 'real' one. So, no deviation in these slave devices - nice.
MFD gains a tad more complexity due to the additional wrapper regmap. That's not bad though. MFD also needs to use the 'unwrapped' register addresses for the slave regmap config (ranges and max register). This won't get extremely ugly though as we can do some simple macros for 'unwrapping'.
What I do dislike is the fact that the register addresses for the secondary slave will now be 9 bits. This will require some modifications in the power-supply driver, which currently stores the addresses using u8. The register values can still be 8-bits though, so maybe it won't get that bad. I haven't tested this yet.
As a result, I am not entirely convinced, but not totally against this idea either.
I'll be away for a bit more than a week, starting from Friday, so it may be I won't spin the next version until around the last days of the October.
Yours,
-- Matti.