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i2c-algo-bit: Fix spurious SCL timeouts under heavy load

When the system is under heavy load, there can be a significant delay
between the getscl() and time_after() calls inside sclhi(). That delay
may cause the time_after() check to trigger after SCL has gone high,
causing sclhi() to return -ETIMEDOUT.

To fix the problem, double check that SCL is still low after the
timeout has been reached, before deciding to return -ETIMEDOUT.

Signed-off-by: Ville Syrjala <>
Signed-off-by: Jean Delvare <>
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Ville Syrjala Jean Delvare
Ville Syrjala authored and Jean Delvare committed Mar 15, 2012
1 parent 834aa6f commit 8ee161ce5e0cfc689eb677f227a6248191165fac
Showing with 7 additions and 1 deletion.
  1. +7 −1 drivers/i2c/algos/i2c-algo-bit.c
@@ -103,8 +103,14 @@ static int sclhi(struct i2c_algo_bit_data *adap)
* chips may hold it low ("clock stretching") while they
* are processing data internally.
- if (time_after(jiffies, start + adap->timeout))
+ if (time_after(jiffies, start + adap->timeout)) {
+ /* Test one last time, as we may have been preempted
+ * between last check and timeout test.
+ */
+ if (getscl(adap))
+ break;
return -ETIMEDOUT;
+ }
#ifdef DEBUG

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