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

BugLink: http://bugs.launchpad.net/bugs/959470

commit 8ee161ce5e0cfc689eb677f227a6248191165fac upstream.

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>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/i2c/algos/i2c-algo-bit.c b/drivers/i2c/algos/i2c-algo-bit.c
index eca3bcc4599..f2ce8c36816 100644
--- 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