this is important in cases where client driver
wants to know how many bytes were actually
transferred.

There is one trick here: if transfer is completed,
meaning I2C_CNT reaches zero, then ARDY will be
asserted to let SW know that it can program a
new transfer.

When ARDY is asserted, I2C_CNT is reset to the
original value (msg->len), which means that
for a successful message, msg->transferred = msg->len
and we don't need to spend time with a register
read.

In case of NACK condition, however, I2C_CNT will
remain with the end value which is the amount of
data transferred until NACK condition found on the
bus inclusive. In this situation, msg->transferred
needs to be initialized with:

msg->len - read(I2C_CNT) - 1;

This patch implements exactly that handling.

Signed-off-by: Felipe Balbi <redacted>
---
 drivers/i2c/busses/i2c-omap.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index 699fa12..d268e92 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c

@@ -588,6 +588,9 @@ static int omap_i2c_xfer_msg(struct i2c_adapter *adap,
 		goto out;
 	}
 
+	msg->transferred = msg->len;
+	wmb();