i2c: Allow I2C devices to NAK start events

Add a return value to the event handler.  Some I2C devices will
NAK if they have no data, so allow them to do this.  This required
the following changes:

Go through all the event handlers and change them to return int
and return 0.

Modify i2c_start_transfer to terminate the transaction on a NAK.

Modify smbus handing to not assert if a NAK occurs on a second
operation, and terminate the transaction and return -1 instead.

Add some information on semantics to I2CSlaveClass.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/hw/misc/tmp105.c b/hw/misc/tmp105.c
index f5c2472..04e8378 100644
--- a/hw/misc/tmp105.c
+++ b/hw/misc/tmp105.c
@@ -176,7 +176,7 @@ static int tmp105_tx(I2CSlave *i2c, uint8_t data)
     return 0;
 }
 
-static void tmp105_event(I2CSlave *i2c, enum i2c_event event)
+static int tmp105_event(I2CSlave *i2c, enum i2c_event event)
 {
     TMP105State *s = TMP105(i2c);
 
@@ -185,6 +185,7 @@ static void tmp105_event(I2CSlave *i2c, enum i2c_event event)
     }
 
     s->len = 0;
+    return 0;
 }
 
 static int tmp105_post_load(void *opaque, int version_id)