[v3,next-next] drivers: net: davinci_mdio: prevent spurious timeout

Message ID 20180509154515.5968-1-nsekhar@ti.com
State New
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Series
  • [v3,next-next] drivers: net: davinci_mdio: prevent spurious timeout
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Commit Message

Sekhar Nori May 9, 2018, 3:45 p.m.
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.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

Signed-off-by: Sekhar Nori <nsekhar@ti.com>

---
v3: simplify return path based on comment 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, 8 insertions(+), 7 deletions(-)

-- 
2.16.2

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Comments

Grygorii Strashko May 9, 2018, 8:36 p.m. | #1
On 05/09/2018 10:45 AM, Sekhar Nori wrote:
> 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.

> 

> Reviewed-by: Andrew Lunn <andrew@lunn.ch>

> Signed-off-by: Sekhar Nori <nsekhar@ti.com>

> ---

> v3: simplify return path based on comment 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.

> 


Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>




-- 
regards,
-grygorii
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David Miller May 10, 2018, 9:23 p.m. | #2
From: Sekhar Nori <nsekhar@ti.com>

Date: Wed, 9 May 2018 21:15:15 +0530

> 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.

> 

> Reviewed-by: Andrew Lunn <andrew@lunn.ch>

> Signed-off-by: Sekhar Nori <nsekhar@ti.com>


Applied.
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Patch

diff --git a/drivers/net/ethernet/ti/davinci_mdio.c b/drivers/net/ethernet/ti/davinci_mdio.c
index 3c33f4504d8e..98a1c97fb95e 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 +228,14 @@  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;
-	}
-	dev_err(data->dev, "timed out waiting for idle\n");
-	return -ETIMEDOUT;
+	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;
 }
 
 static int davinci_mdio_read(struct mii_bus *bus, int phy_id, int phy_reg)