i2c: fix bus recovery stop mode timing

commit cf8ce8b80f8bf9669f6ec4e71e16668430febdac upstream.

The I2C specification states that tsu:sto for standard mode timing must
be at minimum 4us. Pictographically, this is:

SCL: ____/~~~~~~~~~
SDA: _________/~~~~
       ->|    |<- 4us minimum

We are currently waiting 2.5us between asserting SCL and SDA, which is
in violation of the standard. Adjust the timings to ensure that we meet
what is stipulated as the minimum timings to ensure that all devices
correctly interpret the STOP bus transition.

This is more important than trying to generate a square wave with even
duty cycle.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 5f6a4985f2bc8f3398bd0dd353e79c213ea50ae9..810a942eaa8e7acb8c760d13ea2b9883b3a8d27e 100644 (file)
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -186,10 +186,11 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
         * If we can set SDA, we will always create a STOP to ensure additional
         * pulses will do no harm. This is achieved by letting SDA follow SCL
         * half a cycle later. Check the 'incomplete_write_byte' fault injector
-        * for details.
+        * for details. Note that we must honour tsu:sto, 4us, but lets use 5us
+        * here for simplicity.
         */
        bri->set_scl(adap, scl);
-       ndelay(RECOVERY_NDELAY / 2);
+       ndelay(RECOVERY_NDELAY);
        if (bri->set_sda)
                bri->set_sda(adap, scl);
        ndelay(RECOVERY_NDELAY / 2);
@@ -211,7 +212,13 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
                scl = !scl;
                bri->set_scl(adap, scl);
                /* Creating STOP again, see above */
-               ndelay(RECOVERY_NDELAY / 2);
+               if (scl)  {
+                       /* Honour minimum tsu:sto */
+                       ndelay(RECOVERY_NDELAY);
+               } else {
+                       /* Honour minimum tf and thd:dat */
+                       ndelay(RECOVERY_NDELAY / 2);
+               }
                if (bri->set_sda)
                        bri->set_sda(adap, scl);
                ndelay(RECOVERY_NDELAY / 2);