greybus: esX: encapsulate packing cport id into header

For the ES1 and ES2 host interfaces we encode the CPort ID over
which the message should be sent within the message itself.  The
CPort ID is recorded in unused pad bytes found in the operation
message header in order to avoid introducing misaligned messages.

This patch defines some helper routines to abstract this activity.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/es1.c

@@ -166,6 +166,32 @@ static void free_urb(struct es1_ap_dev *es1, struct urb *urb)
 	usb_free_urb(urb);
 }
 
+/*
+ * We (ab)use the operation-message header pad bytes to transfer the
+ * cport id in order to minimise overhead.
+ */
+static void
+gb_message_cport_pack(struct gb_operation_msg_hdr *header, u16 cport_id)
+{
+	put_unaligned_le16(cport_id, header->pad);
+}
+
+/* Clear the pad bytes used for the CPort id */
+static void gb_message_cport_clear(struct gb_operation_msg_hdr *header)
+{
+	put_unaligned_le16(0, header->pad);
+}
+
+/* Extract the CPort id packed into the header, and clear it */
+static u16 gb_message_cport_unpack(struct gb_operation_msg_hdr *header)
+{
+	u16 cport_id = get_unaligned_le16(header->pad);
+
+	gb_message_cport_clear(header);
+
+	return cport_id;
+}
+
 /*
  * Returns an opaque cookie value if successful, or a pointer coded
  * error otherwise.  If the caller wishes to cancel the in-flight
@@ -195,11 +221,8 @@ static void *message_send(struct greybus_host_device *hd, u16 cport_id,
 	if (!urb)
 		return ERR_PTR(-ENOMEM);
 
-	/*
-	 * We (ab)use the operation-message header pad bytes to transfer the
-	 * cport id in order to minimise overhead.
-	 */
-	put_unaligned_le16(cport_id, message->header->pad);
+	/* Pack the cport id into the message header */
+	gb_message_cport_pack(message->header, cport_id);
 
 	buffer_size = sizeof(*message->header) + message->payload_size;
 
@@ -211,7 +234,7 @@ static void *message_send(struct greybus_host_device *hd, u16 cport_id,
 	if (retval) {
 		pr_err("error %d submitting URB\n", retval);
 		free_urb(es1, urb);
-		put_unaligned_le16(0, message->header->pad);
+		gb_message_cport_clear(message->header);
 		return ERR_PTR(retval);
 	}
 
@@ -365,9 +388,9 @@ static void cport_in_callback(struct urb *urb)
 		goto exit;
 	}
 
+	/* Extract the CPort id, which is packed in the message header */
 	header = urb->transfer_buffer;
-	cport_id = get_unaligned_le16(header->pad);
-	put_unaligned_le16(0, header->pad);
+	cport_id = gb_message_cport_unpack(header);
 
 	if (cport_id_valid(cport_id))
 		greybus_data_rcvd(hd, cport_id, urb->transfer_buffer,
@@ -390,8 +413,7 @@ static void cport_out_callback(struct urb *urb)
 	struct es1_ap_dev *es1 = hd_to_es1(hd);
 	int status = check_urb_status(urb);
 
-	/* Clear the pad bytes used for the cport id */
-	put_unaligned_le16(0, message->header->pad);
+	gb_message_cport_clear(message->header);
 
 	/*
 	 * Tell the submitter that the message send (attempt) is

drivers/staging/greybus/es2.c

@@ -166,6 +166,32 @@ static void free_urb(struct es1_ap_dev *es1, struct urb *urb)
 	usb_free_urb(urb);
 }
 
+/*
+ * We (ab)use the operation-message header pad bytes to transfer the
+ * cport id in order to minimise overhead.
+ */
+static void
+gb_message_cport_pack(struct gb_operation_msg_hdr *header, u16 cport_id)
+{
+	put_unaligned_le16(cport_id, header->pad);
+}
+
+/* Clear the pad bytes used for the CPort id */
+static void gb_message_cport_clear(struct gb_operation_msg_hdr *header)
+{
+	put_unaligned_le16(0, header->pad);
+}
+
+/* Extract the CPort id packed into the header, and clear it */
+static u16 gb_message_cport_unpack(struct gb_operation_msg_hdr *header)
+{
+	u16 cport_id = get_unaligned_le16(header->pad);
+
+	gb_message_cport_clear(header);
+
+	return cport_id;
+}
+
 /*
  * Returns an opaque cookie value if successful, or a pointer coded
  * error otherwise.  If the caller wishes to cancel the in-flight
@@ -195,11 +221,8 @@ static void *message_send(struct greybus_host_device *hd, u16 cport_id,
 	if (!urb)
 		return ERR_PTR(-ENOMEM);
 
-	/*
-	 * We (ab)use the operation-message header pad bytes to transfer the
-	 * cport id in order to minimise overhead.
-	 */
-	put_unaligned_le16(cport_id, message->header->pad);
+	/* Pack the cport id into the message header */
+	gb_message_cport_pack(message->header, cport_id);
 
 	buffer_size = sizeof(*message->header) + message->payload_size;
 
@@ -211,7 +234,7 @@ static void *message_send(struct greybus_host_device *hd, u16 cport_id,
 	if (retval) {
 		pr_err("error %d submitting URB\n", retval);
 		free_urb(es1, urb);
-		put_unaligned_le16(0, message->header->pad);
+		gb_message_cport_clear(message->header);
 		return ERR_PTR(retval);
 	}
 
@@ -365,9 +388,9 @@ static void cport_in_callback(struct urb *urb)
 		goto exit;
 	}
 
+	/* Extract the CPort id, which is packed in the message header */
 	header = urb->transfer_buffer;
-	cport_id = get_unaligned_le16(header->pad);
-	put_unaligned_le16(0, header->pad);
+	cport_id = gb_message_cport_unpack(header);
 
 	if (cport_id_valid(cport_id))
 		greybus_data_rcvd(hd, cport_id, urb->transfer_buffer,
@@ -390,8 +413,7 @@ static void cport_out_callback(struct urb *urb)
 	struct es1_ap_dev *es1 = hd_to_es1(hd);
 	int status = check_urb_status(urb);
 
-	/* Clear the pad bytes used for the cport id */
-	put_unaligned_le16(0, message->header->pad);
+	gb_message_cport_clear(message->header);
 
 	/*
 	 * Tell the submitter that the message send (attempt) is