[PATCH v2 3/3] i2c: cadence: Check for errata condition involving master receive

From: Harini Katakam
Date: Wed Dec 03 2014 - 07:36:31 EST

Cadence I2C controller has the following bugs:
- completion indication is not given to the driver at the end of
a read/receive transfer with HOLD bit set.
- Invalid read transaction are generated on the bus when HW timeout
condition occurs with HOLD bit set.

As a result of the above, if a set of messages to be transferred with
repeated start includes any transfer following a read transfer,
completion is never indicated and timeout occurs.
Hence a check is implemented to return -EOPNOTSUPP for such sequences.

Signed-off-by: Harini Katakam <harinik@xxxxxxxxxx>
Signed-off-by: Vishnu Motghare <vishnum@xxxxxxxxxx>

Dont defeteature repeated start. Just check for unsupported conditions in the
driver and return error.

drivers/i2c/busses/i2c-cadence.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
index 67077c2..f5437e2 100644
--- a/drivers/i2c/busses/i2c-cadence.c
+++ b/drivers/i2c/busses/i2c-cadence.c
@@ -522,6 +522,17 @@ static int cdns_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
* processed with a repeated start.
if (num > 1) {
+ /*
+ * This controller does not give completion interrupt after a
+ * master receive transfer if HOLD bit is set (repeated start),
+ * resulting in SW timeout. Hence, if a receive transfer is
+ * followed by any other transfer, an error is returned
+ * indicating that this sequence is not supported.
+ */
+ for (count = 0; count < num-1; count++) {
+ if (msgs[count].flags & I2C_M_RD)
+ return -EOPNOTSUPP;
+ }
id->bus_hold_flag = 1;
reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
reg |= CDNS_I2C_CR_HOLD;

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/