linux-kernel - Re: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller

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Date:   Tue, 9 Jun 2020 11:15:20 -0600
From:   Rob Herring <robh@...nel.org>
To:     Michael Walle <michael@...le.cc>
Cc:     Mark Brown <broonie@...nel.org>, Lee Jones <lee.jones@...aro.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        david.m.ertman@...el.com, shiraz.saleem@...el.com,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-hwmon@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-watchdog@...r.kernel.org,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld
 management controller

On Tue, Jun 09, 2020 at 05:01:17PM +0200, Michael Walle wrote:
> Am 2020-06-09 16:42, schrieb Mark Brown:
> > On Tue, Jun 09, 2020 at 04:38:31PM +0200, Michael Walle wrote:
> > 
> > >   mfd-device@10 {
> > >     compatible = "simple-regmap", "simple-mfd";
> > >     reg = <10>;
> > >     regmap,reg-bits = <8>;
> > >     regmap,val-bits = <8>;
> > >     sub-device@0 {
> > >       compatible = "vendor,sub-device0";
> > >       reg = <0>;
> > >     };
> > 
> > A DT binding like this is not a good idea, encoding the details of the
> > register map into the DT binding makes it an ABI which is begging for
> > trouble.  I'd also suggest that any device using a generic driver like
> > this should have a specific compatible string for the device so we can
> > go back and add quirks later if we need them.
> 
> Like in the spidev case, yes. But OTOH if I _just_ encode the parameters
> for the regmap a MFD, Lee don't agree because its just a shim. So either
> way I seem to be stuck here.
> 
> Where should I put the code to create an i2c driver, init a regmap and
> populate its childen?

Find another driver doing this already and rename it 'simple-mfd' (no 
relation to the DT binding) and add your compatible string to it. 
'Generic' or 'simple' drivers don't require generic/simple DT bindings.

Or extend the existing syscon driver to look up the bus_type and create 
the regmap based on the bus type?

Rob