[PATCH 9/9] I2C: mv64xxx: fix race between FSM/interrupt and process context

[Russell King]

Asking for a multi-part message to be handled by this driver is racy; it
has been observed that the following sequence is possible with this
driver:

	- send start
	- send address + write
	- send data
	- send (repeated) start
	- send address + write
	- send (repeated) start
	- send address + read
	- unrecoverable bus hang (except by system reset)

The problem is that the interrupt handling sees the next event after the
first repeated start is sent - the IFLG bit is set in the register even
though INTEN is disabled.

Let's fix this by moving all of the message processing into interrupt
context, rather than having it partly in IRQ and partly in process
context.  This allows us to move immediately to the next message in the
interrupt handler and get on with the transfer, rather than incuring a
couple of scheduling switches to get the next message.

Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
 drivers/i2c/busses/i2c-mv64xxx.c |   54 ++++++++++++++++++++++++--------------
 1 files changed, 34 insertions(+), 20 deletions(-)

diff --git a/drivers/i2c/busses/i2c-mv64xxx.c b/drivers/i2c/busses/i2c-mv64xxx.c
index 7457ef5..a2e4633 100644
--- a/drivers/i2c/busses/i2c-mv64xxx.c
+++ b/drivers/i2c/busses/i2c-mv64xxx.c
@@ -86,6 +86,8 @@ enum {
 };
 
 struct mv64xxx_i2c_data {
+	struct i2c_msg		*msgs;
+	int			num_msgs;
 	int			irq;
 	u32			state;
 	u32			action;
@@ -194,7 +196,7 @@ mv64xxx_i2c_fsm(struct mv64xxx_i2c_data *drv_data, u32 status)
 		if ((drv_data->bytes_left == 0)
 				|| (drv_data->aborting
 					&& (drv_data->byte_posn != 0))) {
-			if (drv_data->send_stop) {
+			if (drv_data->send_stop || drv_data->aborting) {
 				drv_data->action = MV64XXX_I2C_ACTION_SEND_STOP;
 				drv_data->state = MV64XXX_I2C_STATE_IDLE;
 			} else {
@@ -271,12 +273,25 @@ mv64xxx_i2c_do_action(struct mv64xxx_i2c_data *drv_data)
 {
 	switch(drv_data->action) {
 	case MV64XXX_I2C_ACTION_SEND_RESTART:
+		/* We should only get here if we have further messages */
+		BUG_ON(drv_data->num_msgs == 0);
+
 		drv_data->cntl_bits |= MV64XXX_I2C_REG_CONTROL_START;
-		drv_data->cntl_bits &= ~MV64XXX_I2C_REG_CONTROL_INTEN;
 		writel(drv_data->cntl_bits,
 			drv_data->reg_base + MV64XXX_I2C_REG_CONTROL);
-		drv_data->block = 0;
-		wake_up(&drv_data->waitq);
+
+		drv_data->msgs++;
+		drv_data->num_msgs--;
+
+		/* Setup for the next message */
+		mv64xxx_i2c_prepare_for_io(drv_data, drv_data->msgs);
+
+		/*
+		 * We're never at the start of the message here, and by this
+		 * time it's already too late to do any protocol mangling.
+		 * Thankfully, do not advertise support for that feature.
+		 */
+		drv_data->send_stop = drv_data->num_msgs == 1;
 		break;
 
 	case MV64XXX_I2C_ACTION_CONTINUE:
@@ -412,20 +427,15 @@ mv64xxx_i2c_wait_for_completion(struct mv64xxx_i2c_data *drv_data)
 
 static int
 mv64xxx_i2c_execute_msg(struct mv64xxx_i2c_data *drv_data, struct i2c_msg *msg,
-				int is_first, int is_last)
+				int is_last)
 {
 	unsigned long	flags;
 
 	spin_lock_irqsave(&drv_data->lock, flags);
 	mv64xxx_i2c_prepare_for_io(drv_data, msg);
 
-	if (is_first) {
-		drv_data->action = MV64XXX_I2C_ACTION_SEND_START;
-		drv_data->state = MV64XXX_I2C_STATE_WAITING_FOR_START_COND;
-	} else {
-		drv_data->action = MV64XXX_I2C_ACTION_SEND_ADDR_1;
-		drv_data->state = MV64XXX_I2C_STATE_WAITING_FOR_ADDR_1_ACK;
-	}
+	drv_data->action = MV64XXX_I2C_ACTION_SEND_START;
+	drv_data->state = MV64XXX_I2C_STATE_WAITING_FOR_START_COND;
 
 	drv_data->send_stop = is_last;
 	drv_data->block = 1;
@@ -453,16 +463,20 @@ static int
 mv64xxx_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
 {
 	struct mv64xxx_i2c_data *drv_data = i2c_get_adapdata(adap);
-	int	i, rc;
+	int rc, ret = num;
 
-	for (i = 0; i < num; i++) {
-		rc = mv64xxx_i2c_execute_msg(drv_data, &msgs[i],
-						i == 0, i + 1 == num);
-		if (rc < 0)
-			return rc;
-	}
+	BUG_ON(drv_data->msgs != NULL);
+	drv_data->msgs = msgs;
+	drv_data->num_msgs = num;
+
+	rc = mv64xxx_i2c_execute_msg(drv_data, &msgs[0], num == 1);
+	if (rc < 0)
+		ret = rc;
+
+	drv_data->num_msgs = 0;
+	drv_data->msgs = NULL;
 
-	return num;
+	return ret;
 }
 
 static const struct i2c_algorithm mv64xxx_i2c_algo = {
-- 
1.7.4.4