[PATCH RFC v1 3/3] clk: Add handling of clk parent and rate assigned from DT

[Grant Likely]

On Sun, 23 Feb 2014 16:48:26 -0800, Mike Turquette <mturquette at linaro.org> wrote:
> Quoting Sylwester Nawrocki (2014-02-21 02:38:21)
> > On 20/02/14 15:09, Grant Likely wrote:
> > [...]
> > >> > diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> > >> > index 7c52c29..d618498 100644
> > >> > --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
> > >> > +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> > >> > @@ -115,3 +115,27 @@ clock signal, and a UART.
> > >> >    ("pll" and "pll-switched").
> > >> >  * The UART has its baud clock connected the external oscillator and its
> > >> >    register clock connected to the PLL clock (the "pll-switched" signal)
> > >> > +
> > >> > +==Static initial configuration of clock parent and clock frequency==
> > >> > +
> > >> > +Some platforms require static configuration of (parts of) the clock controller
> > >> > +often determined by the board design. Such a configuration can be specified in
> > >> > +a clock consumer node through [clk-name]-clk-parent and [clk-name]-clk-rate DT
> > >> > +properties. The former should contain phandle and clock specifier of the parent
> > >> > +clock, the latter the required clock's frequency value (one cell). "clk-name"
> > >> > +should be listed in the clock-names property and a phandle and a clock specifier
> > >> > +pair corresponding to it should be present in the clocks property.
> > >> > +
> > >> > +    uart at a000 {
> > >> > +        compatible = "fsl,imx-uart";
> > >> > +        reg = <0xa000 0x1000>;
> > >> > +  ...
> > >> > +        clocks = <&clkcon 0>, <&clkcon 3>;
> > >> > +        clock-names = "baud", "mux";
> > >> > +
> > >> > +  mux-clk-parent = <&pll 1>;
> > >> > +  baud-clk-rate = <460800>;
> > >
> > > This mixes patterns for references to clocks. Plus it requires composing
> > > property names which is a little painful. I'd rather see a list of
> > > tuples to match the existing pattern already in use
> > > 
> > >       clocks = <&clkcon 0>, <&clkcon 3>;
> > >       clock-names = "baud", "mux";
> > >       clock-parents = <0> <&pll 1>;
> > >       clock-rates = <0> <460800>;
> > 
> > Thank you for the review. This looks much better to me. My bad, I wasn't 
> > aware 0 can be used to denote an empty phandle like this. ePAPR seems not 
> > to be specifying exact meaning of the 'phandle' property values, except 
> > they be unique. Anyway, it seems to be clearly documented within the
> > __of_parse_phandle_with_args() function. 
> > 
> > I'll try this modified binding instead, presumably it would be useful to 
> > have a variant of __of_parse_phandle_with_args() function which would 
> > accept a context data containing result of previous call within an iteration, 
> > similarly as of_property_next_string() is written. So we don't iterate 
> > from beginning of the list with each __of_parse_phandle_with_args() call. 
> > But it's an optimization issue that could be considered separately I guess.
> 
> I was always partial to the regulator style of blahblah-supply but
> Grant's suggestion is much cleaner with respect to the rest of the clock
> binding.
> 
> I guess it will be a bit ugly if a very long array is needed with a
> sparse attribute. E.g. 20 clocks specified in the 'clocks' property and
> only a single clock needs to have its parent or rate specified.
> 
> Is there a reason not to support both methods?

Yes. Complexity. Having two ways to do it is far worse to maintain.

g.