i2c: omap: Trigger bus recovery in lockup case

A very conservative check for bus activity (to prevent interference
in multimaster setups) prevented the bus recovery methods from being
triggered in the case that SDA or SCL was stuck low.
This defeats the purpose of the recovery mechanism, which was introduced
for exactly this situation (a slave device keeping SDA pulled down).

Also added a check to make sure SDA is low before attempting recovery.
If SDA is not stuck low, recovery will not help, so we can skip it.

Note that bus lockups can persist across reboots. The only other options
are to reset or power cycle the offending slave device, and many i2c
slaves do not even have a reset pin.

If we see that one of the lines is low for the entire timeout duration,
we can actually be sure that there is no other master driving the bus.
It is therefore save for us to attempt a bus recovery.

Signed-off-by: Claudio Foellmi <[e-mail]>
Tested-by: Vignesh R <[e-mail]>
Reviewed-by: Grygorii Strashko <[e-mail]>
[wsa: fixed one return code to -EBUSY]
Signed-off-by: Wolfram Sang <[e-mail]>

drivers/i2c/busses/i2c-omap.c

···
 }
 
 /*
+ * Try bus recovery, but only if SDA is actually low.
+ */
+static int omap_i2c_recover_bus(struct omap_i2c_dev *omap)
+{
+	u16 systest;
+
+	systest = omap_i2c_read_reg(omap, OMAP_I2C_SYSTEST_REG);
+	if ((systest & OMAP_I2C_SYSTEST_SCL_I_FUNC) &&
+	    (systest & OMAP_I2C_SYSTEST_SDA_I_FUNC))
+		return 0; /* bus seems to already be fine */
+	if (!(systest & OMAP_I2C_SYSTEST_SCL_I_FUNC))
+		return -EBUSY; /* recovery would not fix SCL */
+	return i2c_recover_bus(&omap->adapter);
+}
+
+/*
  * Waiting on Bus Busy
  */
 static int omap_i2c_wait_for_bb(struct omap_i2c_dev *omap)
···
 	timeout = jiffies + OMAP_I2C_TIMEOUT;
 	while (omap_i2c_read_reg(omap, OMAP_I2C_STAT_REG) & OMAP_I2C_STAT_BB) {
 		if (time_after(jiffies, timeout))
-			return i2c_recover_bus(&omap->adapter);
+			return omap_i2c_recover_bus(omap);
 		msleep(1);
 	}
 
···
 		}
 
 		if (time_after(jiffies, timeout)) {
+			/*
+			 * SDA or SCL were low for the entire timeout without
+			 * any activity detected. Most likely, a slave is
+			 * locking up the bus with no master driving the clock.
+			 */
 			dev_warn(omap->dev, "timeout waiting for bus ready\n");
-			return -ETIMEDOUT;
+			return omap_i2c_recover_bus(omap);
 		}
 
 		msleep(1);