i2c: davinci: Fix smbus Oops with AIC33 usage

This fixes Oops at kernel startup while "scanning" for TLV320AIC23IDx
addresses.

Additional fix from Sudhakar Rajashekhara: I think 'first byte set'
should come after the write because an I2C transaction is being
carried out before configuring the I2C mode register (which has bits
to configure Master, Start condition etc), which causes undefined
behavior.

Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Alexander Vasiliev <alexvasiljev@gmail.com>
Signed-off-by: Brad Griffis <bgriffis@ti.com>
Signed-off-by: Dirk Behme <dirk.behme@gmail.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>

drivers/i2c/busses/i2c-davinci.c

@@ -113,6 +113,7 @@ struct davinci_i2c_dev {
 	u8			*buf;
 	size_t			buf_len;
 	int			irq;
+	int			stop;
 	u8			terminate;
 	struct i2c_adapter	adapter;
 };
@@ -250,9 +251,6 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
 	u16 w;
 	int r;
 
-	if (msg->len == 0)
-		return -EINVAL;
-
 	if (!pdata)
 		pdata = &davinci_i2c_platform_data_default;
 	/* Introduce a delay, required for some boards (e.g Davinci EVM) */
@@ -264,6 +262,7 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
 
 	dev->buf = msg->buf;
 	dev->buf_len = msg->len;
+	dev->stop = stop;
 
 	davinci_i2c_write_reg(dev, DAVINCI_I2C_CNT_REG, dev->buf_len);
 
@@ -281,6 +280,10 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
 		flag |= DAVINCI_I2C_MDR_TRX;
 	if (stop)
 		flag |= DAVINCI_I2C_MDR_STP;
+	if (msg->len == 0) {
+		flag |= DAVINCI_I2C_MDR_RM;
+		flag &= ~DAVINCI_I2C_MDR_STP;
+	}
 
 	/* Enable receive or transmit interrupts */
 	w = davinci_i2c_read_reg(dev, DAVINCI_I2C_IMR_REG);
@@ -291,9 +294,21 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
 	davinci_i2c_write_reg(dev, DAVINCI_I2C_IMR_REG, w);
 
 	dev->terminate = 0;
+
 	/* write the data into mode register */
 	davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, flag);
 
+	/*
+	 * First byte should be set here, not after interrupt,
+	 * because transmit-data-ready interrupt can come before
+	 * NACK-interrupt during sending of previous message and
+	 * ICDXR may have wrong data
+	 */
+	if ((!(msg->flags & I2C_M_RD)) && dev->buf_len) {
+		davinci_i2c_write_reg(dev, DAVINCI_I2C_DXR_REG, *dev->buf++);
+		dev->buf_len--;
+	}
+
 	r = wait_for_completion_interruptible_timeout(&dev->cmd_complete,
 						      dev->adapter.timeout);
 	if (r == 0) {
@@ -372,7 +387,7 @@ i2c_davinci_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
 
 static u32 i2c_davinci_func(struct i2c_adapter *adap)
 {
-	return I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK);
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
 }
 
 static void terminate_read(struct davinci_i2c_dev *dev)
@@ -431,6 +446,14 @@ static irqreturn_t i2c_davinci_isr(int this_irq, void *dev_id)
 		case DAVINCI_I2C_IVR_ARDY:
 			davinci_i2c_write_reg(dev,
 				DAVINCI_I2C_STR_REG, DAVINCI_I2C_STR_ARDY);
+			if (((dev->buf_len == 0) && (dev->stop != 0)) ||
+			    (dev->cmd_err & DAVINCI_I2C_STR_NACK)) {
+				w = davinci_i2c_read_reg(dev,
+							 DAVINCI_I2C_MDR_REG);
+				w |= DAVINCI_I2C_MDR_STP;
+				davinci_i2c_write_reg(dev,
+						      DAVINCI_I2C_MDR_REG, w);
+			}
 			complete(&dev->cmd_complete);
 			break;