i2c-designware: Divide i2c_dw_xfer_msg into two functions

We have some steps at the top of i2c_dw_xfer_msg() to set up a slave
address and enable DW I2C core.  And it's executed only when we don't
have STATUS_WRITE_IN_PROGRESS.

But we need to make sure that STATUS_WRITE_IN_PROGRESS only indicates
that we have a pending i2c_msg to process.  In other words, even if
STATUS_WRITE_IN_PROGRESS is not set, that doesn't mean we're at initial
state in the I2C transaction.

Since i2c_dw_xfer_msg() will be invoked again and again during a
transaction, those init steps have a possibility to be re-processed
needlessly.  For example, this issue easily takes place when processing
a combined transaction with a certain condition (the number of tx bytes
in the first i2c_msg, equals to the Tx FIFO depth).

Consequently we should not use STATUS_WRITE_IN_PROGRESS to determine
where we're at in an I2C transaction.  It would be better to separate
those initialization steps from i2c_dw_xfer_msg().
Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi@necel.com>
Acked-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

drivers/i2c/busses/i2c-designware.c

@@ -326,6 +326,29 @@ static int i2c_dw_wait_bus_not_busy(struct dw_i2c_dev *dev)
 	return 0;
 }
 
+static void i2c_dw_xfer_init(struct dw_i2c_dev *dev)
+{
+	struct i2c_msg *msgs = dev->msgs;
+	u32 ic_con;
+
+	/* Disable the adapter */
+	writel(0, dev->base + DW_IC_ENABLE);
+
+	/* set the slave (target) address */
+	writel(msgs[dev->msg_write_idx].addr, dev->base + DW_IC_TAR);
+
+	/* if the slave address is ten bit address, enable 10BITADDR */
+	ic_con = readl(dev->base + DW_IC_CON);
+	if (msgs[dev->msg_write_idx].flags & I2C_M_TEN)
+		ic_con |= DW_IC_CON_10BITADDR_MASTER;
+	else
+		ic_con &= ~DW_IC_CON_10BITADDR_MASTER;
+	writel(ic_con, dev->base + DW_IC_CON);
+
+	/* Enable the adapter */
+	writel(1, dev->base + DW_IC_ENABLE);
+}
+
 /*
  * Initiate low level master read/write transaction.
  * This function is called from i2c_dw_xfer when starting a transfer.
@@ -336,7 +359,7 @@ static void
 i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
 {
 	struct i2c_msg *msgs = dev->msgs;
-	u32 ic_con, intr_mask;
+	u32 intr_mask;
 	int tx_limit = dev->tx_fifo_depth - readl(dev->base + DW_IC_TXFLR);
 	int rx_limit = dev->rx_fifo_depth - readl(dev->base + DW_IC_RXFLR);
 	u32 addr = msgs[dev->msg_write_idx].addr;
@@ -344,25 +367,6 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
 
 	intr_mask = DW_IC_INTR_STOP_DET | DW_IC_INTR_TX_ABRT | DW_IC_INTR_RX_FULL;
 
-	if (!(dev->status & STATUS_WRITE_IN_PROGRESS)) {
-		/* Disable the adapter */
-		writel(0, dev->base + DW_IC_ENABLE);
-
-		/* set the slave (target) address */
-		writel(msgs[dev->msg_write_idx].addr, dev->base + DW_IC_TAR);
-
-		/* if the slave address is ten bit address, enable 10BITADDR */
-		ic_con = readl(dev->base + DW_IC_CON);
-		if (msgs[dev->msg_write_idx].flags & I2C_M_TEN)
-			ic_con |= DW_IC_CON_10BITADDR_MASTER;
-		else
-			ic_con &= ~DW_IC_CON_10BITADDR_MASTER;
-		writel(ic_con, dev->base + DW_IC_CON);
-
-		/* Enable the adapter */
-		writel(1, dev->base + DW_IC_ENABLE);
-	}
-
 	for (; dev->msg_write_idx < dev->msgs_num; dev->msg_write_idx++) {
 		/* if target address has changed, we need to
 		 * reprogram the target address in the i2c
@@ -474,6 +478,7 @@ i2c_dw_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
 		goto done;
 
 	/* start the transfers */
+	i2c_dw_xfer_init(dev);
 	i2c_dw_xfer_msg(dev);
 
 	/* wait for tx to complete */