linux-kernel - Re: [RFC] MFD's relationship with Device Tree (OF)

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Date:   Sun, 14 Jun 2020 12:26:30 +0200
From:   Michael Walle <michael@...le.cc>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Mark Brown <broonie@...nel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Robin Murphy <robin.murphy@....com>,
        GregKroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC] MFD's relationship with Device Tree (OF)

Hi Rob,

Am 2020-06-10 00:03, schrieb Rob Herring:
[..]
> Yes, we should use 'reg' whenever possible. If we don't have 'reg',
> then you shouldn't have a unit-address either and you can simply match
> on the node name (standard DT driver matching is with compatible,
> device_type, and node name (w/o unit-address)). We've generally been
> doing 'classname-N' when there's no 'reg' to do 'classname@N'.
> Matching on 'classname-N' would work with node name matching as only
> unit-addresses are stripped.

This still keeps me thinking. Shouldn't we allow the (MFD!) device
driver creator to choose between "classname@N" and "classname-N".
In most cases N might not be made up, but it is arbitrarily chosen;
for example you've chosen the bank for the ab8500 reg. It is not
a defined entity, like an I2C address if your parent is an I2C bus,
or a SPI chip select, or the memory address in case of MMIO. Instead
the device driver creator just chooses some "random" property from
the datasheet; another device creator might have chosen another
property. Wouldn't it make more sense, to just say this MFD provides
N pwm devices and the subnodes are matching based on pwm-{0,1..N-1}?
That would also be the logical consequence of the current MFD sub
device to OF node matching code, which just supports N=1.

-michael