Re: [RFC PATCH net-next v3 15/20] net: dsa: qca8k: dsa: qca8k: protect MASTER busy_wait with mdio mutex

MDIO_MASTER operation have a dedicated busy wait that is not protected
by the mdio mutex. This can cause situation where the MASTER operation
is done and a normal operation is executed between the MASTER read/write
and the MASTER busy_wait. Rework the qca8k_mdio_read/write function to
address this issue by binding the lock for the whole MASTER operation
and not only the mdio read/write common operation.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
---
 drivers/net/dsa/qca8k.c | 69 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 57 insertions(+), 12 deletions(-)

diff --git a/drivers/net/dsa/qca8k.c b/drivers/net/dsa/qca8k.c
index b21835d719b5..27234dd4c74a 100644
--- a/drivers/net/dsa/qca8k.c
+++ b/drivers/net/dsa/qca8k.c

@@ -633,9 +633,33 @@ qca8k_port_to_phy(int port)
 	return port - 1;
 }
 
+static int
+qca8k_mdio_busy_wait(struct qca8k_priv *priv, u32 reg, u32 mask)
+{
+	unsigned long timeout;
+	u16 r1, r2, page;
+
+	qca8k_split_addr(reg, &r1, &r2, &page);
+
+	timeout = jiffies + msecs_to_jiffies(20);
+
+	/* loop until the busy flag has cleared */
+	do {
+		u32 val = qca8k_mii_read32(priv->bus, 0x10 | r2, r1);
+		int busy = val & mask;
+
+		if (!busy)
+			break;
+		cond_resched();
+	} while (!time_after_eq(jiffies, timeout));

+
+	return time_after_eq(jiffies, timeout);
+}
+
 static int
 qca8k_mdio_write(struct qca8k_priv *priv, int port, u32 regnum, u16 data)
 {
+	u16 r1, r2, page;
 	u32 phy, val;
 	int ret;
 

@@ -651,12 +675,22 @@ qca8k_mdio_write(struct qca8k_priv *priv, int port, u32 regnum, u16 data)
 	      QCA8K_MDIO_MASTER_REG_ADDR(regnum) |
 	      QCA8K_MDIO_MASTER_DATA(data);
 
-	ret = qca8k_write(priv, QCA8K_MDIO_MASTER_CTRL, val);
+	qca8k_split_addr(QCA8K_MDIO_MASTER_CTRL, &r1, &r2, &page);
+
+	mutex_lock_nested(&priv->bus->mdio_lock, MDIO_MUTEX_NESTED);
+
+	ret = qca8k_set_page(priv->bus, page);
 	if (ret)
-		return ret;
+		goto exit;
 
-	ret = qca8k_busy_wait(priv, QCA8K_MDIO_MASTER_CTRL,
-			      QCA8K_MDIO_MASTER_BUSY);
+	qca8k_mii_write32(priv->bus, 0x10 | r2, r1, val);
+
+	if (qca8k_mdio_busy_wait(priv, QCA8K_MDIO_MASTER_CTRL,
+				 QCA8K_MDIO_MASTER_BUSY))
+		ret = -ETIMEDOUT;