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 <syrjala@sci.fi>
Cc: stable@vger.kernel.org
Signed-off-by: Jean Delvare <khali@linux-fr.org>

diff --git a/drivers/i2c/algos/i2c-algo-bit.c b/drivers/i2c/algos/i2c-algo-bit.c
index 525c734..24f94f4 100644 (file)
--- a/drivers/i2c/algos/i2c-algo-bit.c
+++ b/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;
+               }
                cond_resched();
        }
 #ifdef DEBUG