linux-kernel - Re: [DT Question] "simple-mfd" DT binding

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Date:   Tue, 23 May 2017 10:21:49 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Lee Jones <lee.jones@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [DT Question] "simple-mfd" DT binding

Hi Lee, Linus,

Thanks for your comments!

2017-05-22 17:43 GMT+09:00 Linus Walleij <linus.walleij@...aro.org>:
> On Mon, May 22, 2017 at 3:29 AM, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
>
>> Because "simple-bus" indicates that child nodes are
>> simply memory mapped, but the node "register-bit-led"
>> can not be memory-mapped.
>> So, "simple-mfd" can not be replaced "simple-bus" here.
>
> Yeah... just like Lee points out, you are spot on, this is exactly
> the reason why we created "simple-mfd" in the first place
> IIRC.

OK, Linux treats simple-bus and simple-mfd in the same way
as far as I see drivers/of/platform.c

Perhaps, can we document the difference between simple-bus and
simple-mfd clearly?
For example, "Unlike simple-bus, it is legitimate that simple-mfd has
subnodes without reg property"


I think this is typical when "simple-mfd" is used together with "syscon".
The child devices will use regmap of the parent node.
I'd like to be sure this is valid usage.


-- 
Best Regards
Masahiro Yamada