i2c: Add asserts for second smbus i2c_start_transfer()

Some SMBus operations restart the transfer to convert from
write to read mode without an intervening i2c_end_transfer().
The second call cannot fail, so the return code is unchecked,
but this causes Coverity to complain.  So add some asserts
and documentation about this.

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>

2 files changed, 15 insertions, 4 deletions

diff --git a/hw/i2c/core.c b/hw/i2c/core.c
index bd8f16759d..abd4c4cddb 100644
--- a/hw/i2c/core.c
+++ b/hw/i2c/core.c
@@ -88,7 +88,12 @@ int i2c_bus_busy(I2CBus *bus)
     return !QLIST_EMPTY(&bus->current_devs);
 }
 
-/* Returns non-zero if the address is not valid.  */
+/*
+ * Returns non-zero if the address is not valid.  If this is called
+ * again without an intervening i2c_end_transfer(), like in the SMBus
+ * case where the operation is switched from write to read, this
+ * function will not rescan the bus and thus cannot fail.
+ */
 /* TODO: Make this handle multiple masters.  */
 int i2c_start_transfer(I2CBus *bus, uint8_t address, int recv)
 {
diff --git a/hw/i2c/smbus.c b/hw/i2c/smbus.c
index 3979b3dad7..5b4dd3eba4 100644
--- a/hw/i2c/smbus.c
+++ b/hw/i2c/smbus.c
@@ -248,7 +248,9 @@ int smbus_read_byte(I2CBus *bus, uint8_t addr, uint8_t command)
         return -1;
     }
     i2c_send(bus, command);
-    i2c_start_transfer(bus, addr, 1);
+    if (i2c_start_transfer(bus, addr, 1)) {
+        assert(0);
+    }
     data = i2c_recv(bus);
     i2c_nack(bus);
     i2c_end_transfer(bus);
@@ -273,7 +275,9 @@ int smbus_read_word(I2CBus *bus, uint8_t addr, uint8_t command)
         return -1;
     }
     i2c_send(bus, command);
-    i2c_start_transfer(bus, addr, 1);
+    if (i2c_start_transfer(bus, addr, 1)) {
+        assert(0);
+    }
     data = i2c_recv(bus);
     data |= i2c_recv(bus) << 8;
     i2c_nack(bus);
@@ -302,7 +306,9 @@ int smbus_read_block(I2CBus *bus, uint8_t addr, uint8_t command, uint8_t *data)
         return -1;
     }
     i2c_send(bus, command);
-    i2c_start_transfer(bus, addr, 1);
+    if (i2c_start_transfer(bus, addr, 1)) {
+        assert(0);
+    }
     len = i2c_recv(bus);
     if (len > 32) {
         len = 0;