[PATCH v2 3/3] net: ethernet: fec: fix refclk enable for SMSC LAN8710/20

[Richard Leitner <dev@g0hl1n.net>]

From: Richard Leitner <richard.leitner@skidata.com>

Some PHYs (for example the SMSC LAN8710/LAN8720) doesn't allow turning
the refclk on and off again during operation (according to their
datasheet). Nonetheless exactly this behaviour was introduced for power
saving reasons by commit e8fcfcd5684a ("net: fec: optimize the clock management to save power").
Therefore after enabling the refclk we detect if an affected PHY is
attached. If so reset and initialize it again.

For a better understanding here's a outline of the time response of the
clock and reset lines before and after this patch:

			  v--fec_probe()              v--fec_enet_open()
			  v                           v
	w/o patch eCLK: ___||||||||____________________|||||||||||||||||
	w/o patch nRST: ----__------------------------------------------
	w/o patch CONF: _______XX_______________________________________

	w/  patch eCLK: ___||||||||____________________|||||||||||||||||
	w/  patch nRST: ----__-----------------------------__-----------
	w/  patch CONF: _______XX_____________________________XX________
			  ^                           ^
			  ^--fec_probe()              ^--fec_enet_open()

Generally speaking this issue is only relevant if the ref clk for the
PHY is generated by the SoC. In our specific case (PCB) this problem
does occur at about every 10th to 50th POR of an LAN8710 connected to an
i.MX6DL SoC. The typical symptom of this problem is a "swinging"
ethernet link. Similar issues were reported by users of the NXP forum:
	https://community.nxp.com/thread/389902
	https://community.nxp.com/message/309354
With this patch applied the issue didn't occur for at least a few
hundret PORs of our board.

Fixes: e8fcfcd5684a ("net: fec: optimize the clock management to save power")
Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
---
 drivers/net/ethernet/freescale/fec_main.c | 37 +++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 06a7caca0cee..52ec9b29a70e 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -68,6 +68,7 @@
 
 static void set_multicast_list(struct net_device *ndev);
 static void fec_enet_itr_coal_init(struct net_device *ndev);
+static int fec_reset_phy(struct net_device *ndev);
 
 #define DRIVER_NAME	"fec"
 
@@ -1833,6 +1834,32 @@ static int fec_enet_mdio_write(struct mii_bus *bus, int mii_id, int regnum,
 	return ret;
 }
 
+static int fec_enet_clk_ref_enable_reset_phy_quirk(struct net_device *ndev)
+{
+	struct phy_device *phy_dev = ndev->phydev;
+	u32 real_phy_id;
+	int ret;
+
+	/* some PHYs need a reset after the refclk was enabled, so we
+	 * reset them here
+	 */
+	if (!phy_dev)
+		return 0;
+	if (!phy_dev->drv)
+		return 0;
+	real_phy_id = phy_dev->drv->phy_id & phy_dev->drv->phy_id_mask;
+	switch (real_phy_id) {
+	case 0x0007c0f0: /* SMSC LAN8710/LAN8720 */
+		ret = fec_reset_phy(ndev);
+		if (ret)
+			return ret;
+		ret = phy_init_hw(phy_dev);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
 static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
 {
 	struct fec_enet_private *fep = netdev_priv(ndev);
@@ -1862,6 +1889,10 @@ static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
 		ret = clk_prepare_enable(fep->clk_ref);
 		if (ret)
 			goto failed_clk_ref;
+
+		ret = fec_enet_clk_ref_enable_reset_phy_quirk(ndev);
+		if (ret)
+			netdev_warn(ndev, "Resetting PHY failed, connection may be unstable\n");
 	} else {
 		clk_disable_unprepare(fep->clk_ahb);
 		clk_disable_unprepare(fep->clk_enet_out);
@@ -2860,11 +2891,17 @@ fec_enet_open(struct net_device *ndev)
 	if (ret)
 		goto err_enet_mii_probe;
 
+	/* as the PHY is connected now, trigger the reset quirk again */
+	ret = fec_enet_clk_ref_enable_reset_phy_quirk(ndev);
+	if (ret)
+		netdev_warn(ndev, "Resetting PHY failed, connection may be unstable\n");
+
 	if (fep->quirks & FEC_QUIRK_ERR006687)
 		imx6q_cpuidle_fec_irqs_used();
 
 	napi_enable(&fep->napi);
 	phy_start(ndev->phydev);
+
 	netif_tx_start_all_queues(ndev);
 
 	device_set_wakeup_enable(&ndev->dev, fep->wol_flag &
-- 
2.11.0