[PATCH] i2c-davinci: Handle signals gracefully

Mike Looijmans
2014-03-14T06:42:52Z

When a signal is caught while the i2c-davinci bus driver is transferring,
the drive just "abandons" the transfer and leaves the controller to fend
for itself. The next I2C transaction will find the controller in an
undefined state and often results in a stream of "initiating i2c bus recovery"
messages until the controller arrives in a defined state. This behaviour
also sends out "half" or possibly even mixed messages to I2C client
devices which may put them in an undesired state as well.

This patch fixes this issue by always attempting to finish the current
transaction, and only abort on bus errors. This keeps the controller in a
defined state, and is also much friendlier towards client devices, because
it will only send complete messages.

Before this patch, reading an I2C device in a loop and interrupting it
often resulted in a "initiating i2c bus recovery" storm and not being
able to communicate via I2C for several seconds. With this patch, I2C
transactions will not be interrupted or otherwise halfway completed.

v2: Completely ignore signals.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
---
drivers/i2c/busses/i2c-davinci.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
index af0b583..254d897 100644
--- a/drivers/i2c/busses/i2c-davinci.c
+++ b/drivers/i2c/busses/i2c-davinci.c
@@ -372,9 +372,9 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
flag |= DAVINCI_I2C_MDR_STP;
davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, flag);

- r = wait_for_completion_interruptible_timeout(&dev->cmd_complete,
+ r = wait_for_completion_timeout(&dev->cmd_complete,
dev->adapter.timeout);
- if (r == 0) {
+ if (unlikely(r == 0)) {
dev_err(dev->dev, "controller timed out\n");
davinci_i2c_recover_bus(dev);
i2c_davinci_init(dev);
@@ -384,7 +384,6 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
if (dev->buf_len) {
/* This should be 0 if all bytes were transferred
* or dev->cmd_err denotes an error.
- * A signal may have aborted the transfer.
*/
if (r >= 0) {
dev_err(dev->dev, "abnormal termination buf_len=%i\n",
@@ -436,22 +435,24 @@ i2c_davinci_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
ret = i2c_davinci_wait_bus_not_busy(dev, 1);
if (ret < 0) {
dev_warn(dev->dev, "timeout waiting for bus ready\n");
- return ret;
+ goto error;
}

for (i = 0; i < num; i++) {
ret = i2c_davinci_xfer_msg(adap, &msgs[i], (i == (num - 1)));
- dev_dbg(dev->dev, "%s [%d/%d] ret: %d\n", __func__, i + 1, num,
- ret);
+ dev_dbg(dev->dev, "%s [%d/%d] %#x ret: %d\n", __func__, i + 1,
+ num, msgs[i].addr, ret);
if (ret < 0)
- return ret;
+ goto error;
}
+ ret = num;

+error:
#ifdef CONFIG_CPU_FREQ
complete(&dev->xfr_complete);
#endif

- return num;
+ return ret;
}

static u32 i2c_davinci_func(struct i2c_adapter *adap)
--
1.7.9.5