netdev - [PATCH net-next 8/9] lan78xx: fix exception on link speed change

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Message-Id: <20210204113121.29786-9-john.efstathiades@pebblebay.com>
Date:   Thu,  4 Feb 2021 11:31:20 +0000
From:   John Efstathiades <john.efstathiades@...blebay.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     UNGLinuxDriver@...rochip.com, davem@...emloft.net,
        netdev@...r.kernel.org, john.efstathiades@...blebay.com
Subject: [PATCH net-next 8/9] lan78xx: fix exception on link speed change

An exception is sometimes seen when the link speed is changed
from auto-negotiation to a fixed speed, or vice versa. The
exception occurs when the MAC is reset (due to the link speed
change) at the same time as the PHY state machine is accessing
a PHY register.

Add serialisation to the MAC reset to eliminate the race condition.

Signed-off-by: John Efstathiades <john.efstathiades@...blebay.com>
---
 drivers/net/usb/lan78xx.c | 54 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 48 insertions(+), 6 deletions(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 9bd21d17d6f1..0a6f4765f595 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -1342,6 +1342,52 @@ static int lan78xx_update_flowcontrol(struct lan78xx_net *dev, u8 duplex,
 
 static void lan78xx_rx_urb_submit_all(struct lan78xx_net *dev);
 
+static int lan78xx_mac_reset(struct lan78xx_net *dev)
+{
+	u32 val;
+	int ret;
+	unsigned long start_time = jiffies;
+
+	mutex_lock(&dev->phy_mutex);
+
+	/* confirm MII not busy */
+	ret = lan78xx_phy_wait_not_busy(dev);
+	if (ret < 0)
+		goto done;
+
+	ret = lan78xx_read_reg(dev, MAC_CR, &val);
+	if (unlikely(ret < 0)) {
+		ret = -EIO;
+		goto done;
+	}
+
+	val |= MAC_CR_RST_;
+	ret = lan78xx_write_reg(dev, MAC_CR, val);
+	if (unlikely(ret < 0)) {
+		ret = -EIO;
+		goto done;
+	}
+
+	/* poll for completion */
+
+	do {
+		ret = lan78xx_read_reg(dev, MAC_CR, &val);
+		if (unlikely(ret < 0)) {
+			ret = -EIO;
+			break;
+		}
+		if (!(val & MAC_CR_RST_)) {
+			ret = 0;
+			break;
+		}
+	} while (!time_after(jiffies, start_time + HZ));
+
+done:
+	mutex_unlock(&dev->phy_mutex);
+
+	return ret;
+}
+
 static int lan78xx_link_reset(struct lan78xx_net *dev)
 {
 	struct phy_device *phydev = dev->net->phydev;
@@ -1360,12 +1406,8 @@ static int lan78xx_link_reset(struct lan78xx_net *dev)
 		dev->link_on = false;
 
 		/* reset MAC */
-		ret = lan78xx_read_reg(dev, MAC_CR, &buf);
-		if (unlikely(ret < 0))
-			return -EIO;
-		buf |= MAC_CR_RST_;
-		ret = lan78xx_write_reg(dev, MAC_CR, buf);
-		if (unlikely(ret < 0))
+		ret = lan78xx_mac_reset(dev);
+		if (unlikely(ret != 0))
 			return -EIO;
 
 		del_timer(&dev->stat_monitor);
-- 
2.17.1