tty: make receive_buf() return the amout of bytes received

it makes it simpler to keep track of the amount of
bytes received and simplifies how flush_to_ldisc counts
the remaining bytes. It also fixes a bug of lost bytes
on n_tty when flushing too many bytes via the USB
serial gadget driver.

Tested-by: Stefan Bigler <stefan.bigler@keymile.com>
Tested-by: Toby Gray <toby.gray@realvnc.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/input/serio/serport.c b/drivers/input/serio/serport.c
index 8755f5f3ad37..f3698967edf6 100644
--- a/drivers/input/serio/serport.c
+++ b/drivers/input/serio/serport.c
@@ -120,17 +120,21 @@ static void serport_ldisc_close(struct tty_struct *tty)
  * 'interrupt' routine.
  */
 
-static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *cp, char *fp, int count)
+static unsigned int serport_ldisc_receive(struct tty_struct *tty,
+                const unsigned char *cp, char *fp, int count)
 {
         struct serport *serport = (struct serport*) tty->disc_data;
         unsigned long flags;
         unsigned int ch_flags;
+        int ret = 0;
         int i;
 
         spin_lock_irqsave(&serport->lock, flags);
 
-        if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+        if (!test_bit(SERPORT_ACTIVE, &serport->flags)) {
+                ret = -EINVAL;
                 goto out;
+        }
 
         for (i = 0; i < count; i++) {
                 switch (fp[i]) {
@@ -152,6 +156,8 @@ static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *c
 
 out:
         spin_unlock_irqrestore(&serport->lock, flags);
+
+        return ret == 0 ? count : ret;
 }
 
 /*