tty: Always handle NULL flag ptr

Most line disciplines already handle the undocumented NULL flag
ptr in their .receive_buf method; however, several don't.

Document the NULL flag ptr, and correct handling in the
N_MOUSE, N_GSM0710 and N_R394 line disciplines.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Acked-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/input/serio/serport.c

@@ -124,7 +124,7 @@ static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *c
 {
 	struct serport *serport = (struct serport*) tty->disc_data;
 	unsigned long flags;
-	unsigned int ch_flags;
+	unsigned int ch_flags = 0;
 	int i;
 
 	spin_lock_irqsave(&serport->lock, flags);
@@ -133,18 +133,20 @@ static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *c
 		goto out;
 
 	for (i = 0; i < count; i++) {
-		switch (fp[i]) {
-		case TTY_FRAME:
-			ch_flags = SERIO_FRAME;
-			break;
-
-		case TTY_PARITY:
-			ch_flags = SERIO_PARITY;
-			break;
-
-		default:
-			ch_flags = 0;
-			break;
+		if (fp) {
+			switch (fp[i]) {
+			case TTY_FRAME:
+				ch_flags = SERIO_FRAME;
+				break;
+
+			case TTY_PARITY:
+				ch_flags = SERIO_PARITY;
+				break;
+
+			default:
+				ch_flags = 0;
+				break;
+			}
 		}
 
 		serio_interrupt(serport->serio, cp[i], ch_flags);

drivers/tty/n_gsm.c

@@ -2269,14 +2269,15 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 	char *f;
 	int i;
 	char buf[64];
-	char flags;
+	char flags = TTY_NORMAL;
 
 	if (debug & 4)
 		print_hex_dump_bytes("gsmld_receive: ", DUMP_PREFIX_OFFSET,
 				     cp, count);
 
 	for (i = count, dp = cp, f = fp; i; i--, dp++) {
-		flags = *f++;
+		if (f)
+			flags = *f++;
 		switch (flags) {
 		case TTY_NORMAL:
 			gsm->receive(gsm, *dp);

drivers/tty/n_r3964.c

@@ -1244,7 +1244,7 @@ static void r3964_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 {
 	struct r3964_info *pInfo = tty->disc_data;
 	const unsigned char *p;
-	char *f, flags = 0;
+	char *f, flags = TTY_NORMAL;
 	int i;
 
 	for (i = count, p = cp, f = fp; i; i--, p++) {

include/linux/tty_ldisc.h

@@ -84,7 +84,8 @@
  *	processing.  <cp> is a pointer to the buffer of input
  *	character received by the device.  <fp> is a pointer to a
  *	pointer of flag bytes which indicate whether a character was
- *	received with a parity error, etc.
+ *	received with a parity error, etc. <fp> may be NULL to indicate
+ *	all data received is TTY_NORMAL.
  *
  * void	(*write_wakeup)(struct tty_struct *);
  *
@@ -118,7 +119,8 @@
  *	processing.  <cp> is a pointer to the buffer of input
  *	character received by the device.  <fp> is a pointer to a
  *	pointer of flag bytes which indicate whether a character was
- *	received with a parity error, etc.
+ *	received with a parity error, etc. <fp> may be NULL to indicate
+ *	all data received is TTY_NORMAL.
  *	If assigned, prefer this function for automatic flow control.
  */