linux-kernel - Re: [PATCH v2 3/4] dt-bindings: mfd: Add Delta TN48M CPLD drivers bindings

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Date:   Tue, 1 Jun 2021 15:48:26 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Michael Walle <michael@...le.cc>
Cc:     Robert Marko <robert.marko@...tura.hr>,
        Rob Herring <robh@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        bgolaszewski@...libre.com, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Luka Perkov <luka.perkov@...tura.hr>, jmp@...phyte.org,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        Donald Buczek <buczek@...gen.mpg.de>
Subject: Re: [PATCH v2 3/4] dt-bindings: mfd: Add Delta TN48M CPLD drivers
 bindings

On Tue, 01 Jun 2021, Lee Jones wrote:

> On Tue, 01 Jun 2021, Michael Walle wrote:
> 
> > Am 2021-06-01 10:19, schrieb Lee Jones:
> > > Why do you require one single Regmap anyway?  Are they register banks
> > > not neatly separated on a per-function basis?
> > 
> > AFAIK you can only have one I2C device driver per device, hence the
> > simple-mfd-i2c.
> 
> Sorry, can you provide more detail.

I'd still like further explanation to be sure, but if you mean what I
think you mean then, no, I don't think that's correct.

The point of simple-mfd-i2c is to provide an I2C device offering
multiple functions, but does so via a non-separated/linear register-
set, with an entry point and an opportunity to register its interwoven 
bank of registers via Regmap.

However, if you can get away with not registering your entire register
set as a single Regmap chunk, then all the better.  This will allow
you to use the OF provided 'simple-mfd' compatible instead.

Now, if you're talking about Regmap not supporting multiple
registrations with only a single I2C address, this *may* very well be
the case, but IIRC, I've spoken to Mark about this previously and he
said the extension to make this possible would be trivial.

So we have to take this on a device-by-device basis an decide what is
best at the time of submission.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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