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, 9 insertions, 4 deletions

diff --git a/hw/i2c/smbus.c b/hw/i2c/smbus.c
index 5b4dd3eba4..2d1b79a689 100644
--- a/hw/i2c/smbus.c
+++ b/hw/i2c/smbus.c
@@ -67,7 +67,7 @@ static void smbus_do_write(SMBusDevice *dev)
     }
 }
 
-static void smbus_i2c_event(I2CSlave *s, enum i2c_event event)
+static int smbus_i2c_event(I2CSlave *s, enum i2c_event event)
 {
     SMBusDevice *dev = SMBUS_DEVICE(s);
 
@@ -148,6 +148,8 @@ static void smbus_i2c_event(I2CSlave *s, enum i2c_event event)
             break;
         }
     }
+
+    return 0;
 }
 
 static int smbus_i2c_recv(I2CSlave *s)
@@ -249,7 +251,8 @@ int smbus_read_byte(I2CBus *bus, uint8_t addr, uint8_t command)
     }
     i2c_send(bus, command);
     if (i2c_start_transfer(bus, addr, 1)) {
-        assert(0);
+        i2c_end_transfer(bus);
+        return -1;
     }
     data = i2c_recv(bus);
     i2c_nack(bus);
@@ -276,7 +279,8 @@ int smbus_read_word(I2CBus *bus, uint8_t addr, uint8_t command)
     }
     i2c_send(bus, command);
     if (i2c_start_transfer(bus, addr, 1)) {
-        assert(0);
+        i2c_end_transfer(bus);
+        return -1;
     }
     data = i2c_recv(bus);
     data |= i2c_recv(bus) << 8;
@@ -307,7 +311,8 @@ int smbus_read_block(I2CBus *bus, uint8_t addr, uint8_t command, uint8_t *data)
     }
     i2c_send(bus, command);
     if (i2c_start_transfer(bus, addr, 1)) {
-        assert(0);
+        i2c_end_transfer(bus);
+        return -1;
     }
     len = i2c_recv(bus);
     if (len > 32) {