Re: r8169: RTL8125B restores default LEDSEL values on Link Up, preventing persistent LED configuration

[Heiner Kallweit <hkallweit1@gmail.com>]

On 15.03.2026 02:46, Huan Zhao wrote:
> Hardware: Beelink SER8 mini PC
> NIC: Realtek RTL8125B (XID 0x641, RTL_GIGA_MAC_VER_63, rev 05)
> Kernel: 6.19.6-arch1-1
> Driver: r8169 (in-tree)
> CONFIG_R8169_LEDS=y
> CONFIG_LEDS_TRIGGER_NETDEV=m
> 
> Problem:
> The RTL8125B chip restores its LEDSEL registers to hardware default values
> on every Link Up event. The r8169 driver does not reapply the LED
> configuration after Link Up, making it impossible to persistently configure
> LEDs (e.g. disable them) through the standard kernel LED subsystem.
> 
> Details:
> 
> The Link Up path in the driver is:
> 
>   r8169_phylink_handler()       [r8169_main.c:4757]
>     -> rtl_link_chg_patch()     [r8169_main.c:1597]
>     -> rtl_enable_tx_lpi()
>     -> pm_request_resume()
> 
> rtl_link_chg_patch() has no handling for RTL_GIGA_MAC_VER_63 and does not
> touch the LEDSEL registers. Similarly, rtl_hw_start_8125b() and
> rtl_hw_start_8125_common(), which are called on hardware initialization,
> do not write to any LEDSEL register (LEDSEL0=0x18, LEDSEL1=0x86,
> LEDSEL2=0x84, LEDSEL3=0x96).
> 
> The only driver code that writes LEDSEL registers is rtl8125_set_led_mode()
> in r8169_leds.c, called exclusively from the LED classdev hw_control
> callbacks. Therefore, any LED configuration applied via sysfs is silently
> overwritten by the hardware chip's own firmware on every Link Up event,
> before the driver has a chance to reapply it.
> 
> This was verified by observing that:
> 1. Writing 0x0000 to all LEDSEL registers (via BAR0 MMIO) before Link Up
>    successfully turns off all LEDs.
> 2. After Link Up completes, the LEDSEL registers revert to their hardware
>    defaults, turning the LEDs back on.
> 3. Writing 0x0000 to LEDSEL registers immediately after Link Up (via
>    NetworkManager dispatcher triggered on dhcp4-change) successfully keeps
>    the LEDs off persistently.
> 
> Original LEDSEL register values (hardware defaults) on this machine:
>   LEDSEL0 (0x18) = 0x0002  (LINK_100)
>   LEDSEL1 (0x86) = 0x0028  (LINK_2500 + LINK_1000)
>   LEDSEL2 (0x84) = 0x022b  (ACT + LINK_2500 + LINK_1000 + LINK_100 + LINK_10)
>   LEDSEL3 (0x96) = 0x0020  (LINK_2500)
> 
Thanks for the report. For preparation of a fix it would be helpful to know
whether this behavior is specific to RTL8125B, or whether this applies
to all chip variants supported by the driver.
A reset to defaults after a deep power-saving state I'd understand, but
a reset to power-up defaults on link-up sounds quirky. But maybe it's
not power-up defaults, but link speed specific defaults.

Hau, Javen: As I don't have access to chip documentation, I'd appreciate
a comment from your side. Thanks!