linux-kernel - [PATCH v6] i2c: cadence: Check for errata condition involving master receive

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Message-Id: <1421174099-19839-1-git-send-email-harinik@xilinx.com>
Date:	Wed, 14 Jan 2015 00:04:59 +0530
From:	Harini Katakam <harinik@...inx.com>
To:	wsa@...-dreams.de, mark.rutland@....com
Cc:	michal.simek@...inx.com, soren.brinkmann@...inx.com,
	linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, harinikatakamlinux@...il.com,
	harinik@...inx.com
Subject: [PATCH v6] i2c: cadence: Check for errata condition involving master receive

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 message following a read message,
completion is never indicated and timeout occurs.
Hence a check is implemented to return -EOPNOTSUPP for such sequences.

Signed-off-by: Harini Katakam <harinik@...inx.com>
Signed-off-by: Vishnu Motghare <vishnum@...inx.com>
---

v6:
- Correct if condition - add braces to include both statements.
- Modify comments and warning message.

v5:
Make warning grepable in driver.

v4:
Use single dev_warn and make message grep-able.

v3:
Add warning in case of unsupported transfer.

v2:
Dont defeteature repeated start. Just check for unsupported conditions in the
driver and return error.

---
 drivers/i2c/busses/i2c-cadence.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
index 5f5d4fa..c7be4fb 100644
--- a/drivers/i2c/busses/i2c-cadence.c
+++ b/drivers/i2c/busses/i2c-cadence.c
@@ -541,6 +541,19 @@ 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 message if HOLD bit is set (repeated start),
+		 * resulting in SW timeout. Hence, if a receive message is
+		 * followed by any other message, 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, "Can't do repeated start after a receive message\n");
+				return -EOPNOTSUPP;
+			}
+		}
 		id->bus_hold_flag = 1;
 		reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET);
 		reg |= CDNS_I2C_CR_HOLD;
-- 
1.7.9.5

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