dm: cros_ec: Don't require protocol 3 support

I2C is now deprecated on ARM platforms and there are no devices that use it
with the v3 protocol. We can't require v3 support if we want to support I2C.
Adjust the error handling to suit.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/misc/cros_ec.c

@@ -154,7 +154,9 @@ static int prepare_proto3_response_buffer(struct cros_ec_dev *dev, int din_len)
  * @param dev		CROS-EC device
  * @param dinp          Returns pointer to response data
  * @param din_len       Maximum size of response in bytes
- * @return number of bytes of response data, or <0 if error
+ * @return number of bytes of response data, or <0 if error. Note that error
+ * codes can be from errno.h or -ve EC_RES_INVALID_CHECKSUM values (and they
+ * overlap!)
  */
 static int handle_proto3_response(struct cros_ec_dev *dev,
 				  uint8_t **dinp, int din_len)
@@ -228,7 +230,7 @@ static int send_command_proto3(struct cros_ec_dev *dev,
 
 #ifdef CONFIG_DM_CROS_EC
 	ops = dm_cros_ec_get_ops(dev->dev);
-	rv = ops->packet(dev->dev, out_bytes, in_bytes);
+	rv = ops->packet ? ops->packet(dev->dev, out_bytes, in_bytes) : -ENOSYS;
 #else
 	switch (dev->interface) {
 #ifdef CONFIG_CROS_EC_SPI
@@ -320,7 +322,7 @@ static int send_command(struct cros_ec_dev *dev, uint8_t cmd, int cmd_version,
  *			If not NULL, it will be updated to point to the data
  *			and will always be double word aligned (64-bits)
  * @param din_len       Maximum size of response in bytes
- * @return number of bytes in response, or -1 on error
+ * @return number of bytes in response, or -ve on error
  */
 static int ec_command_inptr(struct cros_ec_dev *dev, uint8_t cmd,
 		int cmd_version, const void *dout, int dout_len, uint8_t **dinp,
@@ -387,7 +389,7 @@ static int ec_command_inptr(struct cros_ec_dev *dev, uint8_t cmd,
  *			It not NULL, it is a place for ec_command() to copy the
  *      data to.
  * @param din_len       Maximum size of response in bytes
- * @return number of bytes in response, or -1 on error
+ * @return number of bytes in response, or -ve on error
  */
 static int ec_command(struct cros_ec_dev *dev, uint8_t cmd, int cmd_version,
 		      const void *dout, int dout_len,