i2c-au1550: properly terminate zero-byte transfers

Zero-bytes transfers would leave the bus transaction unfinished
(no i2c stop is sent), with the following transfer actually
sending the slave address to the previously addressed device,
resulting in weird device failures (e.g. reset minute register
values in my RTC).
This patch instructs the controller to send an I2C STOP right after
the slave address in case of a zero-byte transfer.
Signed-off-by: Manuel Lauss <mano@roarinelk.homelinux.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/i2c/busses/i2c-au1550.c

@@ -105,7 +105,7 @@ wait_master_done(struct i2c_au1550_data *adap)
 }
 
 static int
-do_address(struct i2c_au1550_data *adap, unsigned int addr, int rd)
+do_address(struct i2c_au1550_data *adap, unsigned int addr, int rd, int q)
 {
 	volatile psc_smb_t	*sp;
 	u32			stat;
@@ -134,6 +134,10 @@ do_address(struct i2c_au1550_data *adap, unsigned int addr, int rd)
 	if (rd)
 		addr |= 1;
 
+	/* zero-byte xfers stop immediately */
+	if (q)
+		addr |= PSC_SMBTXRX_STP;
+
 	/* Put byte into fifo, start up master.
 	*/
 	sp->psc_smbtxrx = addr;
@@ -142,7 +146,7 @@ do_address(struct i2c_au1550_data *adap, unsigned int addr, int rd)
 	au_sync();
 	if (wait_ack(adap))
 		return -EIO;
-	return 0;
+	return (q) ? wait_master_done(adap) : 0;
 }
 
 static u32
@@ -262,7 +266,8 @@ au1550_xfer(struct i2c_adapter *i2c_adap, struct i2c_msg *msgs, int num)
 
 	for (i = 0; !err && i < num; i++) {
 		p = &msgs[i];
-		err = do_address(adap, p->addr, p->flags & I2C_M_RD);
+		err = do_address(adap, p->addr, p->flags & I2C_M_RD,
+				 (p->len == 0));
 		if (err || !p->len)
 			continue;
 		if (p->flags & I2C_M_RD)