kern/58083: Ethernet not attached correctly on non-Zybo Zynq boards

[lloyd%must-have-coffee.gen.nz@localhost]

>Number:         58083
>Category:       kern
>Synopsis:       Ethernet not attached correctly on non-Zybo Zynq boards
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Mar 27 01:15:00 +0000 2024
>Originator:     Lloyd Parkes
>Release:        current @ Sun Mar 24 16:06:37 2024 +0000
>Organization:
Must Have Coffee
>Environment:
NetBSD armv7 10.99.10 NetBSD 10.99.10 (GENERIC) #0: Tue Mar 26 13:22:55 NZDT 2024  lloyd%kudzu.must-have-coffee.gen.nz@localhost:/vol/build/zybo/objdir.evbearmv7hf-el/sys/arch/evbarm/compile/GENERIC evbarm

>Description:
The cemac ethernet driver ignores the first PHY it detects because on Zybo boards the Realtek PHY responds at address 0 (incorrectly) as well as address 1 (correctly). 

Unfortunately this means that the cemac ethernet driver will ignore any PHY that correctly responds on only one address. 
>How-To-Repeat:
Boot NetBSD on an ALINX AX7021B, which is a Zynq 7020 based board with Micrel PHYs instead of Realtek ones.

Type "ifconfig -m cemac0" and note that no PHY appears to be present.

>Fix:
Apply the patch at https://www.must-have-coffee.gen.nz/lloyd/zybo2.diff.

This patch adds support for the appropriate FDT bindings to the PHY code in the cemac driver and then specifies the correct PHY address in the Zynq Zybo device tree files.

Thanks to Jared McNeill for pointing me at example code for this.