netdev - [PATCH net-next v3 4/4] net: fec: add phy_reset_after_clk

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Date:   Tue,  5 Dec 2017 14:26:00 +0100
From:   Richard Leitner <dev@...l1n.net>
To:     robh+dt@...nel.org, mark.rutland@....com, fugang.duan@....com,
        andrew@...n.ch, f.fainelli@...il.com, frowand.list@...il.com
Cc:     davem@...emloft.net, geert+renesas@...der.be,
        sergei.shtylyov@...entembedded.com, baruch@...s.co.il,
        david.wu@...k-chips.com, lukma@...x.de, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        richard.leitner@...data.com
Subject: [PATCH net-next v3 4/4] net: fec: add phy_reset_after_clk_enable() support

From: Richard Leitner <richard.leitner@...data.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 add support for the phy_reset_after_clk_enable function from
phylib to mitigate this issue.

Generally speaking this issue is only relevant if the ref clk for the
PHY is generated by the SoC and therefore the PHY is configured to
"REF_CLK In Mode". In our specific case (PCB) this problem does occur at
about every 10th to 50th POR of an LAN8710 connected to an i.MX6SOLO
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@...data.com>
---
 drivers/net/ethernet/freescale/fec_main.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 610573855213..8c3d0fb7db20 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -1862,6 +1862,8 @@ 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;
+
+		phy_reset_after_clk_enable(ndev->phydev);
 	} else {
 		clk_disable_unprepare(fep->clk_ahb);
 		clk_disable_unprepare(fep->clk_enet_out);
@@ -2860,6 +2862,11 @@ fec_enet_open(struct net_device *ndev)
 	if (ret)
 		goto err_enet_mii_probe;
 
+	/* reset phy if needed here, due to the fact this is the first time we
+	 * have the net_device to phy_driver link
+	 */
+	phy_reset_after_clk_enable(ndev->phydev);
+
 	if (fep->quirks & FEC_QUIRK_ERR006687)
 		imx6q_cpuidle_fec_irqs_used();
 
-- 
2.11.0