coresight: Device tree dependency cycle warnings with bidirectional port references

[梁镇]

Hi CoreSight maintainers,

I'm working on adding CoreSight support for [your SoC/platform name] and
encountering dependency cycle warnings during boot when defining the
device tree topology with bidirectional port references.

## Problem Description

When I define the CoreSight topology in device tree with remote-endpoint
properties in both out-ports and in-ports (as shown in some examples),
the kernel reports dependency cycle warnings:

...
[    2.092243] /soc/funnel at d9042000: Fixed dependency cycle(s) with /soc/etf at d9043000
[    2.099843] /soc/funnel at d9042000: Fixed dependency cycle(s) with /soc/etf at d9043000
[    2.107359] /soc/etf at d9043000: Fixed dependency cycle(s) with /soc/funnel at d9042000
[    2.114899] /soc/etf at d9043000: Fixed dependency cycle(s) with /soc/etr at d9044000
[    2.122234] /soc/etf at d9043000: Fixed dependency cycle(s) with /soc/etr at d9044000
[    2.129492] /soc/etr at d9044000: Fixed dependency cycle(s) with /soc/etf at d9043000

## Current Device Tree Structure

                etf: etf at d9043000 {
                        compatible = "arm,coresight-tmc", "arm,primecell";
                        reg = <0x0 0xd9043000 0x0 0x1000>;
                        clocks = <&dummy_clk>;
                        clock-names = "apb_pclk";
                        out-ports {
                                port {
                                        etf_out_port: endpoint {
                                                remote-endpoint = <&etr_in_port>;
                                        };
                                };
                        };
                        in-ports {
                                port {
                                        etf_in_port: endpoint {
                                                remote-endpoint = <&main_funnel_out_port>;
                                        };
                                };
                        };
                };

                etr: etr at d9044000 {
                        compatible = "arm,coresight-tmc", "arm,primecell";
                        reg = <0x0 0xd9044000 0x0 0x1000>;
                        clocks = <&dummy_clk>;
                        clock-names = "apb_pclk";
                        arm,scatter-gather;
                        in-ports {
                                port {
                                        etr_in_port: endpoint {
                                                remote-endpoint = <&etf_out_port>;
                                        };
                                };
                        };
                };

## Questions

The kernel's fw_devlink mechanism detects and "fixes" these cycles,
   but can I avoid them in the device tree definition?

The system works correctly despite the warnings, but I'd like to
understand the proper way to define the topology to avoid these messages.

Thank you for your guidance!

--------------

Best regards,
liangzhen