[PATCH v2 net-next] drivers: net: davinci_mdio: prevent spurious timeout

[Sekhar Nori <nsekhar@xxxxxx>]

A well timed kernel preemption in the time_after() loop
in wait_for_idle() can result in a spurious timeout
error to be returned.

Fix it by using readl_poll_timeout() which takes care of
this issue.

Signed-off-by: Sekhar Nori <nsekhar@xxxxxx>
---
v2: use readl_poll_timeout() per suggestion from Andrew.

The issue has not been personally observed by me, but has
been reported by users. Sending for next-next given the
non-critical nature. There is seems to be no easy way to
reproduce this.

 drivers/net/ethernet/ti/davinci_mdio.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/ti/davinci_mdio.c b/drivers/net/ethernet/ti/davinci_mdio.c
index 3c33f4504d8e..d073432a5dbe 100644
--- a/drivers/net/ethernet/ti/davinci_mdio.c
+++ b/drivers/net/ethernet/ti/davinci_mdio.c
@@ -34,6 +34,7 @@
 #include <linux/clk.h>
 #include <linux/err.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/pm_runtime.h>
 #include <linux/davinci_emac.h>
 #include <linux/of.h>
@@ -227,14 +228,16 @@ static inline int wait_for_user_access(struct davinci_mdio_data *data)
 static inline int wait_for_idle(struct davinci_mdio_data *data)
 {
 	struct davinci_mdio_regs __iomem *regs = data->regs;
-	unsigned long timeout = jiffies + msecs_to_jiffies(MDIO_TIMEOUT);
+	u32 val, ret;
 
-	while (time_after(timeout, jiffies)) {
-		if (__raw_readl(&regs->control) & CONTROL_IDLE)
-			return 0;
+	ret = readl_poll_timeout(&regs->control, val, val & CONTROL_IDLE,
+				 0, MDIO_TIMEOUT * 1000);
+	if (ret) {
+		dev_err(data->dev, "timed out waiting for idle\n");
+		return ret;
 	}
-	dev_err(data->dev, "timed out waiting for idle\n");
-	return -ETIMEDOUT;
+
+	return 0;
 }
 
 static int davinci_mdio_read(struct mii_bus *bus, int phy_id, int phy_reg)
-- 
2.16.2

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