[PATCH] I2C PPC4xx IIC driver: 0-length transaction temporary fix

this patch adds temporary fix for 0-length requests (e.g. SMBUS_QUICK) to PPC4xx
IIC driver. This i2c controller doesn't support such transactions and this patch
just restores previous driver version behavior making SMBUS_QUICK-based bus scan
at least partially usable. This is temporary kludge until correct bit-banging
emulation is implemented.

drivers/i2c/busses/i2c-ibm_iic.c

@@ -455,6 +455,16 @@ static int iic_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
 	}		
 	for (i = 0; i < num; ++i){
 		if (unlikely(msgs[i].len <= 0)){
+			if (num == 1 && !msgs[0].len){
+				/* Special case for I2C_SMBUS_QUICK emulation.
+				 * Although this logic is FAR FROM PERFECT, this 
+				 * is what previous driver version did.
+				 * IBM IIC doesn't support 0-length transactions
+				 * (except bit-banging through IICx_DIRECTCNTL).
+				 */
+				DBG("%d: zero-length msg kludge\n", dev->idx); 
+				return 0;
+			}
 			DBG("%d: invalid len %d in msg[%d]\n", dev->idx, 
 				msgs[i].len, i);
 			return -EINVAL;