[PATCH v2 06/10] net: pcs: xpcs: add ANRESTART support for SGMII link recovery

[Coia Prant <coiaprant@gmail.com>]

On some hardware using the DesignWare XPCS IP (e.g., RK3568 MAC side
SGMII), the PCS does not automatically restart auto-negotiation when the
link goes down and comes back up. Without an explicit ANRESTART, the link
stays down forever.

Add BMCR_ANRESTART in two places:
1. In xpcs_config_aneg_c37_sgmii(), when starting AN, set ANRESTART
   alongside ANENABLE to initiate a fresh negotiation.
2. In xpcs_get_state_c37_sgmii(), when link is down and AN completion is
   detected, clear the interrupt and trigger ANRESTART to restart the
   negotiation process.

This change has been verified on:
- RK3568 (Photonicat board)
- Wangxun NICs (no regression)

Tested-by: Jiawen Wu <jiawenwu@trustnetic.com>
Signed-off-by: Coia Prant <coiaprant@gmail.com>
---
 drivers/net/pcs/pcs-xpcs.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
index 0337e2bcc0125..28e98449e8ac2 100644
--- a/drivers/net/pcs/pcs-xpcs.c
+++ b/drivers/net/pcs/pcs-xpcs.c
@@ -816,9 +816,14 @@ static int xpcs_config_aneg_c37_sgmii(struct dw_xpcs *xpcs,
 	if (ret < 0)
 		return ret;
 
+	/* Clear CL37 AN complete status */
+	ret = xpcs_write(xpcs, MDIO_MMD_VEND2, DW_VR_MII_AN_INTR_STS, 0);
+	if (ret < 0)
+		return ret;
+
 	if (neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED)
 		ret = xpcs_write(xpcs, MDIO_MMD_VEND2, MII_BMCR,
-				 mdio_ctrl | BMCR_ANENABLE);
+				 mdio_ctrl | BMCR_ANENABLE | BMCR_ANRESTART);
 
 	return ret;
 }
@@ -1089,14 +1094,18 @@ static int xpcs_get_state_c37_sgmii(struct dw_xpcs *xpcs,
 			state->duplex = DUPLEX_FULL;
 		else
 			state->duplex = DUPLEX_HALF;
-
 		return 0;
 	}
 
-	/* Clear AN complete status or interrupt */
-	if (state->an_complete)
+	if (state->an_complete) {
+		/* Clear AN complete status or interrupt */
 		xpcs_write(xpcs, MDIO_MMD_VEND2, DW_VR_MII_AN_INTR_STS, 0);
 
+		/* Initiate the next round of AN */
+		xpcs_modify(xpcs, MDIO_MMD_VEND2, MII_BMCR, BMCR_ANRESTART,
+				    BMCR_ANRESTART);
+	}
+
 	return 0;
 }
 
-- 
2.47.3