i2c/i2c_master.h: Change incorrect comment about I2C_TRANSFER return value to indicate that the method returns zero on success rather than the number of bytes transferred.

arch/arm/src/efm32/efm32_i2c.c

@@ -1441,11 +1441,11 @@ static int efm32_i2c_transfer(FAR struct i2c_master_s *dev,
   FAR struct efm32_i2c_priv_s *priv = (struct efm32_i2c_priv_s *)dev;
   int ret = OK;
 
-  ASSERT(count);
+  DEBUGASSERT(count > 0);
 
-  if (count == 0 || msgs == NULL)
+  if (count <= 0 || msgs == NULL)
     {
-      return -1;
+      return -EINVAL;
     }
 
   /* Ensure that address or flags don't change meanwhile */

arch/arm/src/lc823450/lc823450_i2c.c

@@ -967,8 +967,12 @@ static int lc823450_i2c_transfer(FAR struct i2c_master_s *dev,
                                  FAR struct i2c_msg_s *msgs, int count)
 {
   FAR struct lc823450_i2c_priv_s *priv = (struct lc823450_i2c_priv_s *)dev;
+  irqstate_t irqs;
+  int ret = 0;
 
-  if (!msgs || count == 0)
+  DEBUGASSERT(count > 0);
+
+  if (count <= 0 || msgs == NULL)
     {
       i2cerr("ERROR: invalid param, %p %d\n", msgs, count);
       return -EINVAL;
@@ -978,11 +982,6 @@ static int lc823450_i2c_transfer(FAR struct i2c_master_s *dev,
 
   lc823450_i2c_sem_wait(priv);
 
-  irqstate_t irqs;
-  int ret = 0;
-
-  ASSERT(count);
-
   priv->timedout = false;
 
 #ifdef CONFIG_I2C_RESET

arch/arm/src/stm32/stm32_i2c.c

@@ -1583,14 +1583,15 @@ static int stm32_i2c_transfer(FAR struct i2c_master_s *dev, FAR struct i2c_msg_s
                               int count)
 {
   FAR struct stm32_i2c_priv_s *priv = (struct stm32_i2c_priv_s *)dev;
-  stm32_i2c_sem_wait(priv);   /* Ensure that address or flags don't change meanwhile */
   uint32_t status = 0;
 #ifdef I2C1_FSMC_CONFLICT
   uint32_t ahbenr;
 #endif
   int ret = 0;
 
-  ASSERT(count);
+  DEBUGASSERT(count > 0);
+
+  stm32_i2c_sem_wait(priv);   /* Ensure that address or flags don't change meanwhile */
 
 #ifdef I2C1_FSMC_CONFLICT
   /* Disable FSMC that shares a pin with I2C1 (LBAR) */

arch/arm/src/stm32f7/stm32_i2c.c

@@ -2309,7 +2309,7 @@ static int stm32_i2c_process(FAR struct i2c_master_s *dev, FAR struct i2c_msg_s
   int         errval = 0;
   int         waitrc = 0;
 
-  ASSERT(count);
+  DEBUGASSERT(count > 0);
 
   /* Wait for any STOP in progress */
 

arch/arm/src/stm32l4/stm32l4_i2c.c

@@ -2459,7 +2459,7 @@ static int stm32l4_i2c_process(FAR struct i2c_master_s *dev,
   int         errval = 0;
   int         waitrc = 0;
 
-  ASSERT(count);
+  DEBUGASSERT(count > 0);
 
   /* Wait for any STOP in progress */
 

include/nuttx/i2c/i2c_master.h

@@ -121,7 +121,10 @@
  *   count - The number of transfers to perform
  *
  * Returned Value:
- *   The number of transfers completed
+ *   Zero (OK) or positive on success; a negated errno value on failure.
+ *
+ *   Note : some implementations of this interface return the number of
+ *          transfers completed, but others return OK on success.
  *
  ****************************************************************************/