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, 3 insertions, 1 deletions

diff --git a/hw/audio/wm8750.c b/hw/audio/wm8750.c
index 0c6500e96a..f8b5bebfc2 100644
--- a/hw/audio/wm8750.c
+++ b/hw/audio/wm8750.c
@@ -303,7 +303,7 @@ static void wm8750_reset(I2CSlave *i2c)
     s->i2c_len = 0;
 }
 
-static void wm8750_event(I2CSlave *i2c, enum i2c_event event)
+static int wm8750_event(I2CSlave *i2c, enum i2c_event event)
 {
     WM8750State *s = WM8750(i2c);
 
@@ -321,6 +321,8 @@ static void wm8750_event(I2CSlave *i2c, enum i2c_event event)
     default:
         break;
     }
+
+    return 0;
 }
 
 #define WM8750_LINVOL	0x00