[openwrt/openwrt] realtek: pcs: rtl931x: add 2500Base-X mode

[LEDE Commits]

hauke pushed a commit to openwrt/openwrt.git, branch main:
https://git.openwrt.org/cf1f06817ce2c2f518a11ca3d0a89aa1cf2bcb91

commit cf1f06817ce2c2f518a11ca3d0a89aa1cf2bcb91
Author: Jonas Jelonek <jelonek.jonas at gmail.com>
AuthorDate: Tue Feb 10 13:52:20 2026 +0000

    realtek: pcs: rtl931x: add 2500Base-X mode
    
    Add 2500Base-X handling to mode setting which was rejected with
    -ENOTSUPP before. SDK code available to us doesn't have the proper mode
    value. Though by brute-forcing different mode values, 0x2d was found to
    make a 2500Base-X link work.
    
    This was tested with an otherwise correctly configured RTL8221B PHY
    which is automatically switched between 2500Base-X and SGMII in the
    upstream driver. Though, since there was a previous U-Boot setup for the
    PHY in HISGMII mode, it may not be standalone yet.
    
    Signed-off-by: Jonas Jelonek <jelonek.jonas at gmail.com>
    Link: https://github.com/openwrt/openwrt/pull/22014
    Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
---
 target/linux/realtek/files-6.12/drivers/net/pcs/pcs-rtl-otto.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/target/linux/realtek/files-6.12/drivers/net/pcs/pcs-rtl-otto.c b/target/linux/realtek/files-6.12/drivers/net/pcs/pcs-rtl-otto.c
index 713abf68b9..d72477ab0b 100644
--- a/target/linux/realtek/files-6.12/drivers/net/pcs/pcs-rtl-otto.c
+++ b/target/linux/realtek/files-6.12/drivers/net/pcs/pcs-rtl-otto.c
@@ -3148,6 +3148,13 @@ static int rtpcs_931x_sds_set_ip_mode(struct rtpcs_serdes *sds,
 		mode_val = 0x9;
 		break;
 
+	case RTPCS_SDS_MODE_2500BASEX:
+		/* available SDK code doesn't have this value. based on brute-forcing
+		 * the SerDes mode register field until the link is working
+		 */
+		mode_val = 0x2d;
+		break;
+
 	case RTPCS_SDS_MODE_10GBASER:
 		mode_val = 0x35;
 		break;