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 8104aa2..f59c8cd 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c

@@ -594,6 +594,9 @@ static int omap_i2c_xfer_msg(struct i2c_adapter *adap,
 		goto out;
 	}
 
+	msg->transferred = msg->len;
+	wmb();
+
 	if ((dev->cmd_err & OMAP_I2C_STAT_AL)
 			|| (dev->cmd_err & OMAP_I2C_STAT_ROVR)
 			|| (dev->cmd_err & OMAP_I2C_STAT_XUDF)) {

@@ -603,6 +606,15 @@ static int omap_i2c_xfer_msg(struct i2c_adapter *adap,
 	}
 
 	if (dev->cmd_err & OMAP_I2C_STAT_NACK) {
+		/* In case of a NACK, we need to check how many bytes we
+		 * actually transferred, so we can tell our client driver about
+		 * it.
+		 *
+		 * Let's check it here and overwrite msg->transferred.
+		 */
+		w = omap_i2c_read_reg(dev, OMAP_I2C_CNT_REG);
+		msg->transferred = msg->len - w - 1;
+
 		if (msg->flags & I2C_M_IGNORE_NAK)
 			return 0;
 

-- 
1.8.0.rc0