[PATCH RFT] i2c: emev2: avoid race when unregistering slave client

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

After we disabled interrupts, there might still be an active one
running. Sync before clearing the pointer to the slave device.

Fixes: c31d0a00021d ("i2c: emev2: add slave support")
Reported-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---

Not tested on hardware yet. If someone has the board set up, testing if
standard I2C communication works would be nice. That would mean irq
setup did not regress. The actual race is more complicated to trigger.
If noone has the board, I will fetch it from my repository. It is packed
away currently.

 drivers/i2c/busses/i2c-emev2.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-emev2.c b/drivers/i2c/busses/i2c-emev2.c
index 35b302d983e0..959d4912ec0d 100644
--- a/drivers/i2c/busses/i2c-emev2.c
+++ b/drivers/i2c/busses/i2c-emev2.c
@@ -69,6 +69,7 @@ struct em_i2c_device {
 	struct completion msg_done;
 	struct clk *sclk;
 	struct i2c_client *slave;
+	int irq;
 };
 
 static inline void em_clear_set_bit(struct em_i2c_device *priv, u8 clear, u8 set, u8 reg)
@@ -339,6 +340,12 @@ static int em_i2c_unreg_slave(struct i2c_client *slave)
 
 	writeb(0, priv->base + I2C_OFS_SVA0);
 
+	/*
+	 * Wait for interrupt to finish. New slave irqs cannot happen because we
+	 * cleared the slave address and, thus, only extension codes will be
+	 * detected which do not use the slave ptr.
+	 */
+	synchronize_irq(priv->irq);
 	priv->slave = NULL;
 
 	return 0;
@@ -355,7 +362,7 @@ static int em_i2c_probe(struct platform_device *pdev)
 {
 	struct em_i2c_device *priv;
 	struct resource *r;
-	int irq, ret;
+	int ret;
 
 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
 	if (!priv)
@@ -390,8 +397,8 @@ static int em_i2c_probe(struct platform_device *pdev)
 
 	em_i2c_reset(&priv->adap);
 
-	irq = platform_get_irq(pdev, 0);
-	ret = devm_request_irq(&pdev->dev, irq, em_i2c_irq_handler, 0,
+	priv->irq = platform_get_irq(pdev, 0);
+	ret = devm_request_irq(&pdev->dev, priv->irq, em_i2c_irq_handler, 0,
 				"em_i2c", priv);
 	if (ret)
 		goto err_clk;
@@ -401,7 +408,8 @@ static int em_i2c_probe(struct platform_device *pdev)
 	if (ret)
 		goto err_clk;
 
-	dev_info(&pdev->dev, "Added i2c controller %d, irq %d\n", priv->adap.nr, irq);
+	dev_info(&pdev->dev, "Added i2c controller %d, irq %d\n", priv->adap.nr,
+		 priv->irq);
 
 	return 0;
 
-- 
2.20.1