Revert "i2c: rcar: remove spinlock"

This reverts commit 150b8be3.

The I2C core's per-adapter locks can't protect from IRQs, so the driver still
needs a spinlock to protect the register accesses.
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: stable@vger.kernel.org # 3.16+
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-rcar.c

@@ -34,6 +34,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 
 /* register offsets */
 #define ICSCR	0x00	/* slave ctrl */
@@ -95,6 +96,7 @@ struct rcar_i2c_priv {
 	struct i2c_msg	*msg;
 	struct clk *clk;
 
+	spinlock_t lock;
 	wait_queue_head_t wait;
 
 	int pos;
@@ -365,6 +367,9 @@ static irqreturn_t rcar_i2c_irq(int irq, void *ptr)
 	struct rcar_i2c_priv *priv = ptr;
 	u32 msr;
 
+	/*-------------- spin lock -----------------*/
+	spin_lock(&priv->lock);
+
 	msr = rcar_i2c_read(priv, ICMSR);
 
 	/* Only handle interrupts that are currently enabled */
@@ -403,6 +408,9 @@ static irqreturn_t rcar_i2c_irq(int irq, void *ptr)
 		wake_up(&priv->wait);
 	}
 
+	spin_unlock(&priv->lock);
+	/*-------------- spin unlock -----------------*/
+
 	return IRQ_HANDLED;
 }
 
@@ -412,14 +420,21 @@ static int rcar_i2c_master_xfer(struct i2c_adapter *adap,
 {
 	struct rcar_i2c_priv *priv = i2c_get_adapdata(adap);
 	struct device *dev = rcar_i2c_priv_to_dev(priv);
+	unsigned long flags;
 	int i, ret, timeout;
 
 	pm_runtime_get_sync(dev);
 
+	/*-------------- spin lock -----------------*/
+	spin_lock_irqsave(&priv->lock, flags);
+
 	rcar_i2c_init(priv);
 	/* start clock */
 	rcar_i2c_write(priv, ICCCR, priv->icccr);
 
+	spin_unlock_irqrestore(&priv->lock, flags);
+	/*-------------- spin unlock -----------------*/
+
 	ret = rcar_i2c_bus_barrier(priv);
 	if (ret < 0)
 		goto out;
@@ -431,6 +446,9 @@ static int rcar_i2c_master_xfer(struct i2c_adapter *adap,
 			break;
 		}
 
+		/*-------------- spin lock -----------------*/
+		spin_lock_irqsave(&priv->lock, flags);
+
 		/* init each data */
 		priv->msg	= &msgs[i];
 		priv->pos	= 0;
@@ -440,6 +458,9 @@ static int rcar_i2c_master_xfer(struct i2c_adapter *adap,
 
 		ret = rcar_i2c_prepare_msg(priv);
 
+		spin_unlock_irqrestore(&priv->lock, flags);
+		/*-------------- spin unlock -----------------*/
+
 		if (ret < 0)
 			break;
 
@@ -543,6 +564,7 @@ static int rcar_i2c_probe(struct platform_device *pdev)
 
 	irq = platform_get_irq(pdev, 0);
 	init_waitqueue_head(&priv->wait);
+	spin_lock_init(&priv->lock);
 
 	adap = &priv->adap;
 	adap->nr = pdev->id;