[PATCH v2 7/7] i2c: omap: implement handling for 'transferred' bytes

Felipe Balbi
2012-10-25T12:25:15Z

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 <balbi-l0cyMroinI0@public.gmane.org>
---
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();
+
/* We have an error */
if (dev->cmd_err & (OMAP_I2C_STAT_AL | OMAP_I2C_STAT_ROVR |
OMAP_I2C_STAT_XUDF)) {
@@ -597,6 +600,15 @@ 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