[PATCH net v4 1/2] net: ethernet: bgmac: preserve forced 2.5 Gbps link speed

[Florian Fainelli <florian.fainelli@broadcom.com>]

Northstar and Northstar Plus use a 2.5 Gbps internal link between the
AMAC and the switch.  BGMAC_FEAT_FORCE_SPEED_2500 makes bgmac_miiconfig()
configure that speed, but bgmac_adjust_link() subsequently replaces it
with the synthetic fixed PHY's 1 Gbps speed.

Use the forced speed when processing link changes so the MAC remains at
2.5 Gbps.  Together with configuring the switch IMP port for its 2 Gbps
mode, this eliminates the output queue discards that caused approximately
1000 TCP retransmissions per second during an iperf3 transmit test.

Restrict the platform forced-speed flag to Northstar Plus using the SoC
compatible, since Hurricane2 shares the AMAC compatible. Other platform
AMACs without a phy-handle must continue following the fixed PHY speed.
The BCMA path already selects the flag only for the Northstar family.

Fixes: f6a95a24957a ("net: ethernet: bgmac: Add platform device support")
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 drivers/net/ethernet/broadcom/bgmac-platform.c | 3 ++-
 drivers/net/ethernet/broadcom/bgmac.c          | 8 ++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bgmac-platform.c b/drivers/net/ethernet/broadcom/bgmac-platform.c
index 4e266ce41180..4880b1890481 100644
--- a/drivers/net/ethernet/broadcom/bgmac-platform.c
+++ b/drivers/net/ethernet/broadcom/bgmac-platform.c
@@ -243,7 +243,8 @@ static int bgmac_probe(struct platform_device *pdev)
 		bgmac->phy_connect = platform_phy_connect;
 	} else {
 		bgmac->phy_connect = bgmac_phy_connect_direct;
-		bgmac->feature_flags |= BGMAC_FEAT_FORCE_SPEED_2500;
+		if (of_machine_is_compatible("brcm,nsp"))
+			bgmac->feature_flags |= BGMAC_FEAT_FORCE_SPEED_2500;
 	}
 
 	return bgmac_enet_probe(bgmac);
diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
index 669eb7ce7d40..9ef7307edd41 100644
--- a/drivers/net/ethernet/broadcom/bgmac.c
+++ b/drivers/net/ethernet/broadcom/bgmac.c
@@ -1430,11 +1430,15 @@ void bgmac_adjust_link(struct net_device *net_dev)
 {
 	struct bgmac *bgmac = netdev_priv(net_dev);
 	struct phy_device *phy_dev = net_dev->phydev;
+	int speed = phy_dev->speed;
 	bool update = false;
 
+	if (bgmac->feature_flags & BGMAC_FEAT_FORCE_SPEED_2500)
+		speed = SPEED_2500;
+
 	if (phy_dev->link) {
-		if (phy_dev->speed != bgmac->mac_speed) {
-			bgmac->mac_speed = phy_dev->speed;
+		if (speed != bgmac->mac_speed) {
+			bgmac->mac_speed = speed;
 			update = true;
 		}
 
-- 
2.53.0