i2c: bcm2835: Clear current buffer pointers and counts after a transfer

paulkocialkowski · Wolfram Sang · commit f275a4659484 · 2019-02-15T09:45:05.000+01:00
The driver's interrupt handler checks whether a message is currently being handled with the curr_msg pointer. When it is NULL, the interrupt is considered to be unexpected. Similarly, the i2c_start_transfer routine checks for the remaining number of messages to handle in num_msgs. However, these values are never cleared and always keep the message and number relevant to the latest transfer (which might be done already and the underlying message memory might have been freed). When an unexpected interrupt hits with the DONE bit set, the isr will then try to access the flags field of the curr_msg structure, leading to a fatal page fault. The msg_buf and msg_buf_remaining fields are also never cleared at the end of the transfer, which can lead to similar pitfalls. Fix these issues by introducing a cleanup function and always calling it after a transfer is finished. Fixes: e247454 ("i2c: bcm2835: Fix hang for writing messages larger than 16 bytes") Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com> Acked-by: Stefan Wahren <stefan.wahren@i2se.com> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
@@ -183,6 +183,15 @@ static void bcm2835_i2c_start_transfer(struct bcm2835_i2c_dev *i2c_dev)
 	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, c);
 }
 
+static void bcm2835_i2c_finish_transfer(struct bcm2835_i2c_dev *i2c_dev)
+{
+	i2c_dev->curr_msg = NULL;
+	i2c_dev->num_msgs = 0;
+
+	i2c_dev->msg_buf = NULL;
+	i2c_dev->msg_buf_remaining = 0;
+}
+
 /*
  * Note about I2C_C_CLEAR on error:
  * The I2C_C_CLEAR on errors will take some time to resolve -- if you were in
@@ -283,6 +292,9 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 
 	time_left = wait_for_completion_timeout(&i2c_dev->completion,
 						adap->timeout);
+
+	bcm2835_i2c_finish_transfer(i2c_dev);
+
 	if (!time_left) {
 		bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C,
 				   BCM2835_I2C_C_CLEAR);
