Hi,

rockchip,rk3588-cru.yaml, dt-binding for RK3588 clock and reset module,
contains description of customized property "rockchip,grf",

  rockchip,grf:
    $ref: /schemas/types.yaml#/definitions/phandle
    description: >
      phandle to the syscon managing the "general register files". It is
      used for GRF muxes, if missing any muxes present in the GRF will
      not be available.

But after doing some searching, I found that clk-rk3588.c actually
defines no clock hardware with MUXGRF type. This is also true in in the
vendor code[1], it seems there is actually no GRF mux on RK3588
platform.

Best regards,
Yao Zi

[1]: https://github.com/rockchip-linux/kernel/blob/604cec4004abe5a96c734f2fab7b74809d2d742f/drivers/clk/rockchip/clk-rk3588.c