NFC: xmit from hci ops must return 0 or negative

xmit callback provided by a driver encapsulates upper layers
data and sends it to the hardware. So, HCI does not know the
exact amount of data being sent and thus can't handle partially
sent frames properly.

Therefore, the driver must return 0 for completely sent frame or
negative for failure.
Signed-off-by: NWaldemar Rymarkiewicz <waldemar.rymarkiewicz@tieto.com>
Acked-by: NEric Lapuyade <eric.lapuyade@intel.com>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

drivers/nfc/pn544_hci.c

@@ -235,8 +235,12 @@ static int pn544_hci_i2c_write(struct i2c_client *client, u8 *buf, int len)
 		r = i2c_master_send(client, buf, len);
 	}
 
-	if (r >= 0 && r != len)
-		r = -EREMOTEIO;
+	if (r >= 0) {
+		if (r != len)
+			return -EREMOTEIO;
+		else
+			return 0;
+	}
 
 	return r;
 }

include/net/nfc/hci.h

@@ -30,6 +30,11 @@ struct nfc_hci_ops {
 	int (*open) (struct nfc_hci_dev *hdev);
 	void (*close) (struct nfc_hci_dev *hdev);
 	int (*hci_ready) (struct nfc_hci_dev *hdev);
+	/*
+	 * xmit must always send the complete buffer before
+	 * returning. Returned result must be 0 for success
+	 * or negative for failure.
+	 */
 	int (*xmit) (struct nfc_hci_dev *hdev, struct sk_buff *skb);
 	int (*start_poll) (struct nfc_hci_dev *hdev,
 			   u32 im_protocols, u32 tm_protocols);