Re: [PATCH 10/16] clk: Add support for clock nexus dt bindings

[Brian Masney <bmasney@redhat.com>]

On Fri, Mar 27, 2026 at 09:09:32PM +0100, Miquel Raynal (Schneider Electric) wrote:
> A nexus node is some kind of parent device abstracting the outer
> connections. They are particularly useful for describing connectors-like
> interfaces but not only. Certain IP blocks will typically include inner
> blocks and distribute resources to them.
> 
> In the case of clocks, there is already the concept of clock controller,
> but this usually indicates some kind of control over the said clock,
> ie. gate or rate control. When there is none of this, an existing
> approach is to reference the upper clock, which is wrong from a hardware
> point of view.
> 
> Nexus nodes are already part of the device-tree specification and clocks
> are already mentioned:
> https://github.com/devicetree-org/devicetree-specification/blob/v0.4/source/chapter2-devicetree-basics.rst#nexus-nodes-and-specifier-mapping
> 
> Following the introductions of nexus nodes support for interrupts, gpios
> and pwms, here is the same logic applied again to the clk subsystem,
> just by transitioning from of_parse_phandle_with_args() to
> of_parse_phandle_with_args_map():
> 
> * Nexus OF support:
> commit bd6f2fd5a1d5 ("of: Support parsing phandle argument lists through a nexus node")
> * GPIO adoption:
> commit c11e6f0f04db ("gpio: Support gpio nexus dt bindings")
> * PWM adoption:
> commit e71e46a6f19c ("pwm: Add support for pwm nexus dt bindings")
> 
> Expected Nexus properties supported:
> - clock-map: maps inner clocks to inlet clocks,
> - clock-map-mask: specifier cell(s) which will be remapped,
> - clock-map-pass-thru: specifier cell(s) not used for remapping,
>   forwarded as-is.
> 
> In my own usage I had to deal with controllers where clock-map-mask and
> clock-map-pass-thru were not relevant, but here is a made up example
> showing how all these properties could go together:
> 
> Example:
>     soc_clk: clock-controller {
>         #clock-cells = <2>;
>     };
> 
>     container: container {
>         #clock-cells = <2>;
>         clock-map = <0 0 &soc_clk 2 0>,
>                     <1 0 &soc_clk 6 0>;
>         clock-map-mask = <0xffffffff 0x0>;
>         clock-map-pass-thru = <0x0 0xffffffff>;
> 
>         child-device {
>             clocks = <&container 1 0>;
> 	    /* This is equivalent to <&soc_clk 6 0> */
>         };
>     };
> 
> The child device does not need to know about the outer implementation,
> and only knows about what the nexus provides. The nexus acts as a
> pass-through, with no extra control.
> 
> Signed-off-by: Miquel Raynal (Schneider Electric) <miquel.raynal@bootlin.com>
> Reviewed-by: Herve Codina <herve.codina@bootlin.com>

Reviewed-by: Brian Masney <bmasney@redhat.com>