realtek: pcs: rtl931x: fix SerDes link status reading

Fix the function for reading the SerDes link status to work correctly
based on the code the SDK uses. This is mostly for the sake of
documentation and quick access to the information. The function isn't
used currently but may be in the future, thus no functional change here.

Signed-off-by: Jonas Jelonek <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/22014
Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/realtek/files-6.12/drivers/net/pcs/pcs-rtl-otto.c

@@ -3386,12 +3386,22 @@ static int rtpcs_931x_sds_link_sts_get(struct rtpcs_serdes *sds)
 {
 	u32 sts, sts1, latch_sts, latch_sts1;
 
-	if (0) {
+	switch (sds->hw_mode) {
+	case RTPCS_SDS_MODE_XSGMII:
 		sts = rtpcs_sds_read_bits(sds, 0x41, 29, 8, 0);
 		sts1 = rtpcs_sds_read_bits(sds, 0x81, 29, 8, 0);
 		latch_sts = rtpcs_sds_read_bits(sds, 0x41, 30, 8, 0);
 		latch_sts1 = rtpcs_sds_read_bits(sds, 0x81, 30, 8, 0);
-	} else {
+		break;
+
+	case RTPCS_SDS_MODE_SGMII:
+	case RTPCS_SDS_MODE_HISGMII:
+	case RTPCS_SDS_MODE_2500BASEX:
+		sts = rtpcs_sds_read_bits(sds, 0x41, 29, 8, 0);
+		latch_sts = rtpcs_sds_read_bits(sds, 0x41, 30, 8, 0);
+		break;
+
+	default:
 		sts = rtpcs_sds_read_bits(sds, 0x5, 0, 12, 12);
 		latch_sts = rtpcs_sds_read_bits(sds, 0x4, 1, 2, 2);
 		latch_sts1 = rtpcs_sds_read_bits(sds, 0x42, 1, 2, 2);