[PATCH v3 2/2] i2c: cadence: Check for errata condition involving master receive

From: Harini Katakam
Date: Fri Dec 05 2014 - 03:09:00 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>

Add warning in case of unsupported transfer.

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

drivers/i2c/busses/i2c-cadence.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
index 5f5d4fa..3ea3b7a 100644
--- a/drivers/i2c/busses/i2c-cadence.c
+++ b/drivers/i2c/busses/i2c-cadence.c
@@ -541,6 +541,21 @@ 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)
+ dev_warn(adap->dev.parent,
+ "No support for repeated start when\t");
+ dev_warn(adap->dev.parent,
+ "receive is followed by a transfer\n");
+ return -EOPNOTSUPP;
+ }
id->bus_hold_flag = 1;
reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
reg |= CDNS_I2C_CR_HOLD;

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