netdev - [PATCH] net: ethernet: fsl: don't en/disable refclk on open/close

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Message-Id: <20171022131130.8580-1-dev@g0hl1n.net>
Date:   Sun, 22 Oct 2017 15:11:30 +0200
From:   Richard Leitner <dev@...l1n.net>
To:     fugang.duan@....com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Richard Leitner <richard.leitner@...data.com>,
        stable@...r.kernel.org
Subject: [PATCH] net: ethernet: fsl: don't en/disable refclk on open/close

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

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

Some PHYs (for example the LAN8710) doesn't allow turning the ethernet
ref clocks off and on again without reset (according to their datasheet).
Exactly this behaviour was introduced for power saving reasons by
commit e8fcfcd5684a ("net: fec: optimize the clock management to save...")
Therefore remove those en/disables of the refclk during probe, open and
close of the fec.

Generally speaking is this issue only be 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.MX6 SoC. The typical symptom of this problem is a "swinging" ethernet
link. Similar issues were experienced 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
thousand PORs of our board.

Fixes: e8fcfcd5684a ("net: fec: optimize the clock management to sa...")
Cc: stable@...r.kernel.org
Signed-off-by: Richard Leitner <richard.leitner@...data.com>
---
 drivers/net/ethernet/freescale/fec_main.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 3dc2d771a222..8f696b53d8b8 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -2844,9 +2844,6 @@ fec_enet_open(struct net_device *ndev)
 		return ret;
 
 	pinctrl_pm_select_default_state(&fep->pdev->dev);
-	ret = fec_enet_clk_enable(ndev, true);
-	if (ret)
-		goto clk_enable;
 
 	/* I should reset the ring buffers here, but I don't yet know
 	 * a simple way to do that.
@@ -2879,8 +2876,6 @@ fec_enet_open(struct net_device *ndev)
 err_enet_mii_probe:
 	fec_enet_free_buffers(ndev);
 err_enet_alloc:
-	fec_enet_clk_enable(ndev, false);
-clk_enable:
 	pm_runtime_mark_last_busy(&fep->pdev->dev);
 	pm_runtime_put_autosuspend(&fep->pdev->dev);
 	pinctrl_pm_select_sleep_state(&fep->pdev->dev);
@@ -2907,7 +2902,6 @@ fec_enet_close(struct net_device *ndev)
 
 	fec_enet_update_ethtool_stats(ndev);
 
-	fec_enet_clk_enable(ndev, false);
 	pinctrl_pm_select_sleep_state(&fep->pdev->dev);
 	pm_runtime_mark_last_busy(&fep->pdev->dev);
 	pm_runtime_put_autosuspend(&fep->pdev->dev);
@@ -3495,7 +3489,6 @@ fec_probe(struct platform_device *pdev)
 
 	/* Carrier starts down, phylib will bring it up */
 	netif_carrier_off(ndev);
-	fec_enet_clk_enable(ndev, false);
 	pinctrl_pm_select_sleep_state(&pdev->dev);
 
 	ret = register_netdev(ndev);
-- 
2.11.0