[PATCH] I2C: cdns: Fix broken retry mechanism on arbitration lost.

Andrea Merello andrea.merello at iit.it
Fri May 26 16:56:16 CEST 2023

In the current implementation, in case of I2C arbitration lost, a retry is
attempted; the message counter and pointer are reset to the original values
and the I2C xfer process is restart from the beginning.

However the message counter and message pointer are respectively
decremented and incremented by one before attempting any transfer, causing
the 1st transfer not to be actually retried (in case of a single transfer,
nothing is actually retried at all).

This patch fixes this: in case of retry, the 1st transfer is also retried.

Tested on a ZynqMP Kria board, with upstream older u-boot, but the involved
file and underlying logic seem basically the same.

Signed-off-by: Andrea Merello <andrea.merello at iit.it>
 drivers/i2c/i2c-cdns.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-cdns.c b/drivers/i2c/i2c-cdns.c
index 1a89207206..935b2ac637 100644
--- a/drivers/i2c/i2c-cdns.c
+++ b/drivers/i2c/i2c-cdns.c
@@ -444,7 +444,7 @@ static int cdns_i2c_xfer(struct udevice *dev, struct i2c_msg *msg,

 	debug("i2c_xfer: %d messages\n", nmsgs);
 	for (u8 retry = 0; retry < CDNS_I2C_ARB_LOST_MAX_RETRIES &&
-	     nmsgs > 0; nmsgs--, msg++) {
+	     nmsgs > 0;) {
 		debug("i2c_xfer: chip=0x%x, len=0x%x\n", msg->addr, msg->len);
 		if (msg->flags & I2C_M_RD) {
 			ret = cdns_i2c_read_data(i2c_bus, msg->addr, msg->buf,
@@ -461,7 +461,8 @@ static int cdns_i2c_xfer(struct udevice *dev, struct i2c_msg *msg,
+		nmsgs--;
+		msg++;
 		if (ret) {
 			debug("i2c_write: error sending\n");
 			return -EREMOTEIO;

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