linux-kernel - Re: [PATCH 1/2] dt-bindings: Add syscon-names support

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Message-ID: <20191118083952.GB6039@spreadtrum.com>
Date:   Mon, 18 Nov 2019 16:39:52 +0800
From:   Orson Zhai <orson.zhai@...eadtrum.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Orson Zhai <orson.zhai@...soc.com>,
        Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <kevin.tang@...soc.com>
Subject: Re: [PATCH 1/2] dt-bindings: Add syscon-names support

Hi Arnd,

On Fri, Nov 15, 2019 at 10:33:30AM +0100, Arnd Bergmann wrote:
> On Thu, Nov 14, 2019 at 12:48 PM Orson Zhai <orson.zhai@...soc.com> wrote:
> >
> >
> > Make life easier when syscon consumer want to access multiple syscon
> > nodes.
> > Add syscon-names and relative properties to help manage complicated
> > cases when accessing more one syscon node.
> >
> > Signed-off-by: Orson Zhai <orson.zhai@...soc.com>
>
> Hi Orson,
>
> Can you explain why the number of cells in this binding is specific
> to the syscon node rather than the node referencing it?

The story is like this. I found there are too many global registers in
Unisoc(former Spreadtrum) chips. Dozens of offset with dozens of modules
were needed to be specified. So I thought the dts files would seem "horrible"
with a big chunk of syscon-xxx (say more than 20 lines)

I learned from reg-names way which might look clean to hold all these mess things.
But to implement this, the users need to konw the cell-size if we add arguments to syscon node.
I thought to add cell-size into every syscon consumer node is a duplicated work and
I wanted to take advantage of of_parse_phandle_with_args.
So the bindings were created then.


>
> In most other bindings that follow the same scheme, the additional
> arguments are interpreted by the subsystem that is being referenced,
> but the syscon driver is just a simple driver with no subsystem and no
> code to interpret those arguments.

You're correct. I've realized it is narraw to pass here.

>
> The way would otherwise handle the example from your binding
> would be with two separate properties in the display node, like
>
> syscon-enable = <&ap_apb_regs 0x4 0xf00>;
> syscon-power = <&aon_regs 0x8>;

This is an option for consumers all the time.
Acturally my patches are not going to replace this.
I'd like to provide another option to save people like desperate engineers in Spreadtrum :)

>
> in which case, the syscon driver does not need to know anything

Whould it be better if I add syscon-cells into consumer's node?
Then I could read the cell size and use "of_parse_phandle_with_fixed_args()" instead.
This will not involve syscon node itself at all.

Best Regards,
-Orson
> about how it's being used, and the display driver is the one making
> sense of the arguments according to its own binding.
>
> I assume you have some good reason for introducing the other
> approach, but I don't understand it from your submission.
>
>        Arnd
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