linux-kernel - Re: [RFC] clk: vc5: Add bindings for output configurations

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Message-ID: <CAL_JsqL2F3_QPEgG89X_nNgcUDW1Q8tSPBbqVr319T5N0bBiSw@mail.gmail.com>
Date:   Mon, 6 Apr 2020 10:12:11 -0600
From:   Rob Herring <robh@...nel.org>
To:     Adam Ford <aford173@...il.com>
Cc:     devicetree <devicetree@...r.kernel.org>,
        Adam Ford-BE <aford@...conembedded.com>,
        Charles Stevens <charles.stevens@...icpd.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] clk: vc5: Add bindings for output configurations

On Sat, Apr 4, 2020 at 7:38 PM Adam Ford <aford173@...il.com> wrote:
>
> On Sat, Apr 4, 2020 at 8:28 PM Rob Herring <robh@...nel.org> wrote:
> >
> > On Thu, Mar 26, 2020 at 04:32:51PM -0500, Adam Ford wrote:
> > > The Versaclock can be purchased in a non-programmed configuration.
> > > If that is the case, the driver needs to configure the chip to
> > > output the correct signal type, voltage and slew.
> > >
> > > This RFC is proposing an additional binding to allow non-programmed
> > > chips to be configured beyond their default configuration.
> > >
> > > Signed-off-by: Adam Ford <aford173@...il.com>
> > >
> > > diff --git a/Documentation/devicetree/bindings/clock/idt,versaclock5.txt b/Documentation/devicetree/bindings/clock/idt,versaclock5.txt
> > > index 05a245c9df08..4bc46ed9ba4a 100644
> > > --- a/Documentation/devicetree/bindings/clock/idt,versaclock5.txt
> > > +++ b/Documentation/devicetree/bindings/clock/idt,versaclock5.txt
> > > @@ -30,6 +30,25 @@ Required properties:
> > >               - 5p49v5933 and
> > >               - 5p49v5935: (optional) property not present or "clkin".
> > >
> > > +For all output ports, an option child node can be used to specify:
> > > +
> > > +- mode: can be one of
> > > +               - LVPECL: Low-voltage positive/psuedo emitter-coupled logic
> > > +               - CMOS
> > > +               - HCSL
> > > +               - LVDS: Low voltage differential signal
> > > +
> > > +- voltage-level:  can be one of the following microvolts
> > > +               - 1800000
> > > +               - 2500000
> > > +               - 3300000
> > > +-  slew: Percent of normal, can be one of
> > > +               - P80
> > > +               - P85
> > > +               - P90
> > > +               - P100
> > > +
> > > +
> > >  ==Mapping between clock specifier and physical pins==
> > >
> > >  When referencing the provided clock in the DT using phandle and
> > > @@ -62,6 +81,8 @@ clock specifier, the following mapping applies:
> > >
> > >  ==Example==
> > >
> > > +#include <dt-bindings/versaclock.h>
> > > +
> > >  /* 25MHz reference crystal */
> > >  ref25: ref25m {
> > >       compatible = "fixed-clock";
> > > @@ -80,6 +101,13 @@ i2c-master-node {
> > >               /* Connect XIN input to 25MHz reference */
> > >               clocks = <&ref25m>;
> > >               clock-names = "xin";
> > > +
> > > +             ports@1 {
> >
> > 'ports' is already taken as a node name.
> Rob,
>
> The clock chip can drive multiple clocks and each output is
> independent of the rest.  The idea is that port@1 would represent
> output 1, port@2 would represent output 2, etc.
> Is there a name you'd think we should use to represent each output?

clock-output@...?

> Different variations of this chip can have different number of
> outputs.
>
> >
> > > +                     reg = <1>;
> >
> > What do the reg value signify?
>
> I am fine if we drop we drop it. I was under the assumption that reg
> =<1> had to correspond to the port@1 and that it was required since
> other devices with port sub-nodes use the reg entry.

I wasn't suggesting dropping it. Just what 0, 1, 2, etc. corresponds
to as you explained above. Just put that into the 'reg' description.

> > > +                     mode = <CMOS>;
> > > +                     pwr_sel = <1800000>;
> >
> > Not documented. Don't use '-' in property names.
>
> Do you have a preference to what name or convention you want us to use?

Errr, that was supposed to say '_'. Using hyphens is fine.

Also, needs a vendor prefix and if that's in microvolts needs a unit suffix.

Rob