linux-kernel - Re: [PATCH v2 2/4] dt-bindings: ARM: Mediatek: Document devicetree bindings for clock controllers

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Date:	Thu, 2 Jul 2015 12:26:45 +0800
From:	Daniel Kurtz <djkurtz@...omium.org>
To:	James Liao <jamesjj.liao@...iatek.com>
Cc:	"open list:OPEN FIRMWARE AND..." <devicetree@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	srv_heupstream <srv_heupstream@...iatek.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ricky Liang <jcliang@...omium.org>,
	Rob Herring <robh+dt@...nel.org>,
	linux-mediatek@...ts.infradead.org,
	Sascha Hauer <kernel@...gutronix.de>,
	Matthias Brugger <matthias.bgg@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/4] dt-bindings: ARM: Mediatek: Document devicetree
 bindings for clock controllers

On Thu, Jul 2, 2015 at 10:52 AM, James Liao <jamesjj.liao@...iatek.com> wrote:
> Hi Daniel,
>
>> > +Required Properties:
>> > +
>> > +- compatible: Should be:
>> > +       - "mediatek,mt8173-imgsys", "syscon"
>> > +- #clock-cells: Must be 1
>> > +
>> > +The imgsys controller uses the common clk binding from
>> > +Documentation/devicetree/bindings/clock/clock-bindings.txt
>> > +The available clocks are defined in dt-bindings/clock/mt*-clk.h.
>> > +
>> > +Example:
>> > +
>> > +imgsys: imgsys@...00000 {
>>
>> Since these nodes will be supplying clocks to the rest of the system,
>> I think the "name" part of each of these should all be
>> "clock-controller", like topckgen and apmixedsys:
>>
>>   imgsys: clock-controller@...00000 {
>
> These subsystems (and topckgen also) also contains other functions such
> as reset controller, which may be implemented in clk/mediatek/ in the
> future. It is suitable to use "clock-controller" as their name?

Hmm,

I don't know the "right way" to do this either.
Pardon me if you've already had these discussions.
I only recently started looking at these clock nodes in detail :-).

I think what we really have in register space is a "syscon", as
described in [0]:
[0] Documentation/devicetree/bindings/mfd/syscon.txt

So, we can define this block of registers as a syscon:

mmsys_syscon: syscon@...00000 {
       compatible = "mediatek,mt8173-mmsys", "syscon";
       reg = <0 0x14000000 0 0x1000>;
};


Then for the clock controller functionality, we create a node with a
"clock-controller" name and a "-clock" compatible, like this:

mmsys_clock: clock-controller {
       compatible = "mediatek,mt8173-mmsys-clock";
       #clock-cells = <1>;
       mediatek,syscon = <&mmsys_syscon>;
};

You could then do:
CLK_OF_DECLARE(mtk_mmsys, "mediatek,mt8173-mmsys-clock", mtk_mmsys_init);


If you want to reuse the same register range for some other
functionality, we could then use a different node, with a different
compatible:

mmsys: reset-controller {
       compatible = "mediatek,mt8173-mmsys-reset";
       mediatek,syscon = <&mmsys_syscon>;
};

What do you think of this approach?

Thanks!
-Dan
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