This bit is necessary to receive packets from the internal PHY.
Without this bit set, no activity occurs on the interface.
Normally u-boot sets this bit, but if u-boot is compiled without
net support, the interface will be up but without any activity.
The vendor SDK sets this bit along with the PHY_ID bits.
Ported from the Linux change at [1] from Da Xu merged in
commit [2].
[1] https://lore.kernel.org/all/20250425192009.1439508-1-da@libre.computer/
[2] b23285e93bef ("net: mdio: mux-meson-gxl: set reversed bit when using internal phy")
Suggested-by: Da Xue <da@libre.computer>
Link: https://lore.kernel.org/r/20250502-u-boot-topic-mdio-mux-gxl-bit28-v1-1-399f6c3db154@linaro.org
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Port the mdio-mux-meson-gxl.c Linux driver introduced in [1],
and adapt it to U-Boot.
This driver is needed to boot U-Boot with Linux DT since v6.4,
since it switched the MDIO mux from the mmio to a proper GXL driver.
[1] 9a24e1ff4326 ("net: mdio: add amlogic gxl mdio mux support")
Link: https://lore.kernel.org/r/20231213-u-boot-gxl-mdio-mux-v2-1-c56bb02a75ea@linaro.org
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
