linux-kernel - [RFC] net: phy: read link status twice when phy_check_link

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Date:   Fri, 26 Jul 2019 17:53:51 +0800
From:   Yonglong Liu <liuyonglong@...wei.com>
To:     <andrew@...n.ch>, <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linuxarm@...wei.com>, <salil.mehta@...wei.com>,
        <yisen.zhuang@...wei.com>, <shiju.jose@...wei.com>
Subject: [RFC] net: phy: read link status twice when phy_check_link_status()

According to the datasheet of Marvell phy and Realtek phy, the
copper link status should read twice, or it may get a fake link
up status, and cause up->down->up at the first time when link up.
This happens more oftem at Realtek phy.

I add a fake status read, and can solve this problem.

I also see that in genphy_update_link(), had delete the fake
read in polling mode, so I don't know whether my solution is
correct.

Or provide a phydev->drv->read_status functions for the phy I
used is more acceptable?

Signed-off-by: Yonglong Liu <liuyonglong@...wei.com>
---
 drivers/net/phy/phy.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index ef7aa73..0c03edc 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -1,4 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0+
+	err = phy_read_status(phydev);
+	if (err)
+		return err;
 /* Framework for configuring and reading PHY devices
  * Based on code in sungem_phy.c and gianfar_phy.c
  *
@@ -525,6 +528,11 @@ static int phy_check_link_status(struct phy_device *phydev)
 
 	WARN_ON(!mutex_is_locked(&phydev->lock));
 
+	/* Do a fake read */
+	err = phy_read(phydev, MII_BMSR);
+	if (err < 0)
+		return err;
+
 	err = phy_read_status(phydev);
 	if (err)
 		return err;
-- 
2.8.1