OK merci pour ton aide

Donc j'ai flashé ta build. mon câble était dans Lan2, durant le flash et la séquence de reboot.
A la fin le port était bien détecté, les led vert/orange allumées et clignotantes, mais coté PC "réseau non identifié".
ensuite j'ai fait ce que tu as indiqué, et voici les logs du début :
root@OpenWrt:~# grep phy:0x05 /sys/kernel/tracing/trace
kmodloader-414 [001] ..... 11.779151: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x06 val:0x8000
kmodloader-414 [001] ..... 11.779270: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x05 val:0x008a
kmodloader-414 [001] ..... 11.779385: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x02 val:0x001c
kmodloader-414 [001] ..... 11.779500: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x03 val:0xcaf3
kmodloader-414 [001] ..... 11.779614: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x02 val:0x001c
kmodloader-414 [001] ..... 11.779729: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x03 val:0xcaf3
kmodloader-414 [001] ..... 11.779843: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x02 val:0x001c
kmodloader-414 [001] ..... 11.779957: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x03 val:0xcaf3
kmodloader-414 [001] ..... 11.780072: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x08 val:0x8000
kmodloader-414 [001] ..... 11.780186: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x02 val:0x001c
kmodloader-414 [001] ..... 11.780301: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x03 val:0xcaf3
kmodloader-414 [001] ..... 12.316424: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x104 val:0x7001
kmodloader-414 [001] ..... 12.316599: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x01 val:0x0008
kmodloader-414 [001] ..... 12.316753: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x08 val:0x8200
kmodloader-414 [001] ..... 12.316906: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x0b val:0x41a4
kmodloader-414 [001] ..... 12.317059: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x15 val:0x0003
kmodloader-414 [001] ..... 12.317212: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x14 val:0x000e
kmodloader-414 [001] ..... 12.317366: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x15 val:0x0003
kmodloader-414 [001] ..... 12.317522: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x3c val:0x0000
kmodloader-414 [001] ..... 12.317677: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x3e val:0x0000
ip-843 [003] ..... 13.914176: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x145 val:0x0000
ip-843 [003] ..... 13.914302: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0x145 val:0x0001
ip-843 [003] ..... 13.944465: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0x145 val:0x0000
ip-843 [003] ..... 13.974586: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0xb820 val:0x0000
ip-843 [003] ..... 13.974699: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xb820 val:0x0010
ip-843 [003] ..... 13.974811: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0xb820 val:0x0010
ip-843 [003] ..... 13.974922: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xb820 val:0x0010
ip-843 [003] ..... 13.975035: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0xb800 val:0x00c0
ip-843 [003] ..... 13.975147: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0x8023
ip-843 [003] ..... 13.975258: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x3802
ip-843 [003] ..... 13.975369: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xb82e
ip-843 [003] ..... 13.975480: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x0001
ip-843 [003] ..... 13.975591: mdio_access: mt7530_dsa-0 read phy:0x05 reg:0xb820 val:0x0010
ip-843 [003] ..... 13.975702: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xb820 val:0x0090
ip-843 [003] ..... 13.975816: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa016
ip-843 [003] ..... 13.975927: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x0000
ip-843 [003] ..... 13.976038: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa012
ip-843 [003] ..... 13.976148: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x0000
ip-843 [003] ..... 13.976259: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa014
ip-843 [003] ..... 13.976370: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.976481: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x8010
ip-843 [003] ..... 13.976592: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.976703: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x801a
ip-843 [003] ..... 13.976814: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.976924: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x801a
ip-843 [003] ..... 13.977035: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.977146: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x801a
ip-843 [003] ..... 13.977257: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.977368: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x801a
ip-843 [003] ..... 13.977478: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.977590: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x801a
ip-843 [003] ..... 13.977701: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.977811: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x801a
ip-843 [003] ..... 13.977922: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.978032: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x801a
ip-843 [003] ..... 13.978143: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xd719
ip-843 [003] ..... 13.978254: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x3bb7
ip-843 [003] ..... 13.978364: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x8014
ip-843 [003] ..... 13.978475: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xf003
ip-843 [003] ..... 13.978586: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xd704
ip-843 [003] ..... 13.978697: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x406e
ip-843 [003] ..... 13.978807: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.978918: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x12db
ip-843 [003] ..... 13.979029: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1800
ip-843 [003] ..... 13.979139: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0x1301
ip-843 [003] ..... 13.979251: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa026
ip-843 [003] ..... 13.979361: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xffff
ip-843 [003] ..... 13.979472: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa024
ip-843 [003] ..... 13.979584: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xffff
ip-843 [003] ..... 13.979695: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa022
ip-843 [003] ..... 13.979806: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xffff
ip-843 [003] ..... 13.979917: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa020
ip-843 [003] ..... 13.980028: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xffff
ip-843 [003] ..... 13.980138: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa006
ip-843 [003] ..... 13.980250: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xffff
ip-843 [003] ..... 13.980361: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa004
ip-843 [003] ..... 13.980472: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xffff
ip-843 [003] ..... 13.980582: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa436 val:0xa002
ip-843 [003] ..... 13.980693: mdio_access: mt7530_dsa-0 write phy:0x05 reg:0xa438 val:0xffff