i2c: rcar: refactor handling of first message

After moving ICMSR handling to interrupt handlers previously to fix a
race condition, we can now also move ICMSR handling for the first
message out of the function to prepare a message. By introducing a
seperate function to initialize the first message, we can not only
remove some code duplication but the remaining code is also easier to
follow. The function to prepare a message is much simpler without ICMSR
handling.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Author: Wolfram Sang

drivers/i2c/busses/i2c-rcar.c

@@ -98,7 +98,6 @@
 #define RCAR_IRQ_STOP	(MST)
 
 #define ID_LAST_MSG	(1 << 0)
-#define ID_FIRST_MSG	(1 << 1)
 #define ID_DONE		(1 << 2)
 #define ID_ARBLOST	(1 << 3)
 #define ID_NACK		(1 << 4)
@@ -333,41 +332,47 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv)
 	return 0;
 }
 
+/*
+ * We don't have a test case but the HW engineers say that the write order of
+ * ICMSR and ICMCR depends on whether we issue START or REP_START. So, ICMSR
+ * handling is outside of this function. First messages clear ICMSR before this
+ * function, interrupt handlers clear the relevant bits after this function.
+ */
 static void rcar_i2c_prepare_msg(struct rcar_i2c_priv *priv)
 {
 	int read = !!rcar_i2c_is_recv(priv);
 
 	priv->pos = 0;
+	priv->flags &= ID_P_MASK;
+
 	if (priv->msgs_left == 1)
 		priv->flags |= ID_LAST_MSG;
 
 	rcar_i2c_write(priv, ICMAR, i2c_8bit_addr_from_msg(priv->msg));
 	if (!priv->atomic_xfer)
 		rcar_i2c_write(priv, ICMIER, read ? RCAR_IRQ_RECV : RCAR_IRQ_SEND);
 
-	/*
-	 * We don't have a test case but the HW engineers say that the write order
-	 * of ICMSR and ICMCR depends on whether we issue START or REP_START. Since
-	 * it didn't cause a drawback for me, let's rather be safe than sorry.
-	 */
-	if (priv->flags & ID_FIRST_MSG) {
-		rcar_i2c_write(priv, ICMSR, 0);
+	if (priv->flags & ID_P_REP_AFTER_RD)
+		priv->flags &= ~ID_P_REP_AFTER_RD;
+	else
 		rcar_i2c_write(priv, ICMCR, RCAR_BUS_PHASE_START);
-	} else {
-		if (priv->flags & ID_P_REP_AFTER_RD)
-			priv->flags &= ~ID_P_REP_AFTER_RD;
-		else
-			rcar_i2c_write(priv, ICMCR, RCAR_BUS_PHASE_START);
-		/* ICMSR is cleared in interrupt handlers */
-	}
+}
+
+static void rcar_i2c_first_msg(struct rcar_i2c_priv *priv,
+			       struct i2c_msg *msgs, int num)
+{
+	priv->msg = msgs;
+	priv->msgs_left = num;
+	rcar_i2c_write(priv, ICMSR, 0); /* must be before preparing msg */
+	rcar_i2c_prepare_msg(priv);
 }
 
 static void rcar_i2c_next_msg(struct rcar_i2c_priv *priv)
 {
 	priv->msg++;
 	priv->msgs_left--;
-	priv->flags &= ID_P_MASK;
 	rcar_i2c_prepare_msg(priv);
+	/* ICMSR handling must come afterwards in the irq handler */
 }
 
 static void rcar_i2c_cleanup_dma(struct rcar_i2c_priv *priv, bool terminate)
@@ -852,11 +857,7 @@ static int rcar_i2c_master_xfer(struct i2c_adapter *adap,
 	for (i = 0; i < num; i++)
 		rcar_i2c_request_dma(priv, msgs + i);
 
-	/* init first message */
-	priv->msg = msgs;
-	priv->msgs_left = num;
-	priv->flags = (priv->flags & ID_P_MASK) | ID_FIRST_MSG;
-	rcar_i2c_prepare_msg(priv);
+	rcar_i2c_first_msg(priv, msgs, num);
 
 	time_left = wait_event_timeout(priv->wait, priv->flags & ID_DONE,
 				     num * adap->timeout);
@@ -906,12 +907,7 @@ static int rcar_i2c_master_xfer_atomic(struct i2c_adapter *adap,
 		goto out;
 
 	rcar_i2c_init(priv);
-
-	/* init first message */
-	priv->msg = msgs;
-	priv->msgs_left = num;
-	priv->flags = (priv->flags & ID_P_MASK) | ID_FIRST_MSG;
-	rcar_i2c_prepare_msg(priv);
+	rcar_i2c_first_msg(priv, msgs, num);
 
 	j = jiffies + num * adap->timeout;
 	do {