[PATCH 07/14] net: axienet: Fix SGMII support

[Andre Przywara]

With SGMII, the MAC and the PHY can negotiate the link speed between
themselves, without the host needing to mediate between them.
Linux recognises this, and will call phylink's mac_config with the speed
member set to SPEED_UNKNOWN (-1).
Currently the axienet driver will bail out and complain about an
unsupported link speed.

Teach axienet's mac_config callback to leave the MAC's speed setting
alone if the requested speed is SPEED_UNKNOWN.

This fixes axienet operation when the hardware is using SGMII.

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
---
 .../net/ethernet/xilinx/xilinx_axienet_main.c | 21 ++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index 8d2b67cbecf9..e83c7b005f50 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -1512,20 +1512,21 @@ static void axienet_mac_config(struct phylink_config *config, unsigned int mode,
 {
 	struct net_device *ndev = to_net_dev(config->dev);
 	struct axienet_local *lp = netdev_priv(ndev);
-	u32 emmc_reg, fcc_reg;
+	u32 fcc_reg, speed_reg = ~0;
 
-	emmc_reg = axienet_ior(lp, XAE_EMMC_OFFSET);
-	emmc_reg &= ~XAE_EMMC_LINKSPEED_MASK;
 
 	switch (state->speed) {
+	case SPEED_UNKNOWN:
+		/* Keep the current MAC speed setting. Used for SGMII. */
+		break;
 	case SPEED_1000:
-		emmc_reg |= XAE_EMMC_LINKSPD_1000;
+		speed_reg = XAE_EMMC_LINKSPD_1000;
 		break;
 	case SPEED_100:
-		emmc_reg |= XAE_EMMC_LINKSPD_100;
+		speed_reg = XAE_EMMC_LINKSPD_100;
 		break;
 	case SPEED_10:
-		emmc_reg |= XAE_EMMC_LINKSPD_10;
+		speed_reg = XAE_EMMC_LINKSPD_10;
 		break;
 	default:
 		dev_err(&ndev->dev,
@@ -1533,7 +1534,13 @@ static void axienet_mac_config(struct phylink_config *config, unsigned int mode,
 		break;
 	}
 
-	axienet_iow(lp, XAE_EMMC_OFFSET, emmc_reg);
+	if (speed_reg != ~0) {
+		u32 emmc_reg = axienet_ior(lp, XAE_EMMC_OFFSET);
+
+		emmc_reg &= ~XAE_EMMC_LINKSPEED_MASK;
+		emmc_reg |= speed_reg;
+		axienet_iow(lp, XAE_EMMC_OFFSET, emmc_reg);
+	}
 
 	fcc_reg = axienet_ior(lp, XAE_FCC_OFFSET);
 	if (state->pause & MLO_PAUSE_TX)
-- 
2.17.1