i2c: rcar: protect against supurious interrupts on V3U

V3U creates spurious interrupts which we need to handle. This costs time
until BUS_PHASE_DATA can be activated which is problematic for Gen2 SoCs
and earlier. Because of this we introduce two interrupt handlers here
which will call a generic main irq function once the timing critical
stuff is done.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-rcar.c

@@ -625,20 +625,11 @@ static bool rcar_i2c_slave_irq(struct rcar_i2c_priv *priv)
  * generated. It turned out that taking a spinlock at the beginning of the ISR
  * was already causing repeated messages. Thus, this driver was converted to
  * the now lockless behaviour. Please keep this in mind when hacking the driver.
+ * R-Car Gen3 seems to have this fixed but earlier versions than R-Car Gen2 are
+ * likely affected. Therefore, we have different interrupt handler entries.
  */
-static irqreturn_t rcar_i2c_irq(int irq, void *ptr)
+static irqreturn_t rcar_i2c_irq(int irq, struct rcar_i2c_priv *priv, u32 msr)
 {
-	struct rcar_i2c_priv *priv = ptr;
-	u32 msr;
-
-	/* Clear START or STOP immediately, except for REPSTART after read */
-	if (likely(!(priv->flags & ID_P_REP_AFTER_RD)))
-		rcar_i2c_write(priv, ICMCR, RCAR_BUS_PHASE_DATA);
-
-	msr = rcar_i2c_read(priv, ICMSR);
-
-	/* Only handle interrupts that are currently enabled */
-	msr &= rcar_i2c_read(priv, ICMIER);
 	if (!msr) {
 		if (rcar_i2c_slave_irq(priv))
 			return IRQ_HANDLED;
@@ -682,6 +673,41 @@ static irqreturn_t rcar_i2c_irq(int irq, void *ptr)
 	return IRQ_HANDLED;
 }
 
+static irqreturn_t rcar_i2c_gen2_irq(int irq, void *ptr)
+{
+	struct rcar_i2c_priv *priv = ptr;
+	u32 msr;
+
+	/* Clear START or STOP immediately, except for REPSTART after read */
+	if (likely(!(priv->flags & ID_P_REP_AFTER_RD)))
+		rcar_i2c_write(priv, ICMCR, RCAR_BUS_PHASE_DATA);
+
+	/* Only handle interrupts that are currently enabled */
+	msr = rcar_i2c_read(priv, ICMSR);
+	msr &= rcar_i2c_read(priv, ICMIER);
+
+	return rcar_i2c_irq(irq, priv, msr);
+}
+
+static irqreturn_t rcar_i2c_gen3_irq(int irq, void *ptr)
+{
+	struct rcar_i2c_priv *priv = ptr;
+	u32 msr;
+
+	/* Only handle interrupts that are currently enabled */
+	msr = rcar_i2c_read(priv, ICMSR);
+	msr &= rcar_i2c_read(priv, ICMIER);
+
+	/*
+	 * Clear START or STOP immediately, except for REPSTART after read or
+	 * if a spurious interrupt was detected.
+	 */
+	if (likely(!(priv->flags & ID_P_REP_AFTER_RD) && msr))
+		rcar_i2c_write(priv, ICMCR, RCAR_BUS_PHASE_DATA);
+
+	return rcar_i2c_irq(irq, priv, msr);
+}
+
 static struct dma_chan *rcar_i2c_request_dma_chan(struct device *dev,
 					enum dma_transfer_direction dir,
 					dma_addr_t port_addr)
@@ -929,6 +955,7 @@ static int rcar_i2c_probe(struct platform_device *pdev)
 	struct i2c_adapter *adap;
 	struct device *dev = &pdev->dev;
 	unsigned long irqflags = 0;
+	irqreturn_t (*irqhandler)(int irq, void *ptr) = rcar_i2c_gen3_irq;
 	int ret;
 
 	/* Otherwise logic will break because some bytes must always use PIO */
@@ -977,8 +1004,10 @@ static int rcar_i2c_probe(struct platform_device *pdev)
 
 	rcar_i2c_write(priv, ICSAR, 0); /* Gen2: must be 0 if not using slave */
 
-	if (priv->devtype < I2C_RCAR_GEN3)
+	if (priv->devtype < I2C_RCAR_GEN3) {
 		irqflags |= IRQF_NO_THREAD;
+		irqhandler = rcar_i2c_gen2_irq;
+	}
 
 	if (priv->devtype == I2C_RCAR_GEN3) {
 		priv->rstc = devm_reset_control_get_exclusive(&pdev->dev, NULL);
@@ -999,7 +1028,7 @@ static int rcar_i2c_probe(struct platform_device *pdev)
 		priv->flags |= ID_P_HOST_NOTIFY;
 
 	priv->irq = platform_get_irq(pdev, 0);
-	ret = devm_request_irq(dev, priv->irq, rcar_i2c_irq, irqflags, dev_name(dev), priv);
+	ret = devm_request_irq(dev, priv->irq, irqhandler, irqflags, dev_name(dev), priv);
 	if (ret < 0) {
 		dev_err(dev, "cannot get irq %d\n", priv->irq);
 		goto out_pm_disable;