From aa1f4fe003d1c8fe2c1eed5a43bcee4b87303d83 Mon Sep 17 00:00:00 2001
From: Joel King <joelking@codeaurora.org>
Date: Wed, 11 Jul 2012 16:18:54 -0700
Subject: [PATCH] msm: tty: update receive room just before writing data to the
 ldisc

There is a corner case in the tty driver where the value of
tty->receive_room is not being updated before writing data to
the line discipline. When this happens, data is lost because
of failure to re-submit any remaining data to the ldisc.

This fix is dependent on a new tty flag that is set only when
the tty driver is used for efs sync betweem the mdm modem and
the applications processor.

CRs-Fixed: 358868
Change-Id: I0ba02980504b4d8187b8c83111c2c883d194efa2
Signed-off-by: Joel King <joelking@codeaurora.org>
---
 drivers/tty/tty_buffer.c      | 29 +++++++++++++++++++++++++++--
 drivers/usb/serial/usb_wwan.c |  1 +
 include/linux/tty.h           |  2 ++
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 6c9b7cd6778..ccbaa6d00dc 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -418,6 +418,8 @@ static void flush_to_ldisc(struct work_struct *work)
 			int count;
 			char *char_buf;
 			unsigned char *flag_buf;
+			unsigned int left = 0;
+			unsigned int max_space;
 
 			count = head->commit - head->read;
 			if (!count) {
@@ -432,10 +434,33 @@ static void flush_to_ldisc(struct work_struct *work)
 			   line discipline as we want to empty the queue */
 			if (test_bit(TTY_FLUSHPENDING, &tty->flags))
 				break;
+
+			/* update receive room */
+			spin_lock(&tty->read_lock);
+			if (tty->update_room_in_ldisc) {
+				if ((tty->read_cnt == N_TTY_BUF_SIZE - 1) &&
+					(tty->receive_room ==
+						N_TTY_BUF_SIZE - 1))
+					tty->rr_bug++;
+				left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
+			}
+			spin_unlock(&tty->read_lock);
+
 			if (!tty->receive_room)
 				break;
-			if (count > tty->receive_room)
-				count = tty->receive_room;
+
+			if (tty->update_room_in_ldisc && !left) {
+				schedule_work(&tty->buf.work);
+				break;
+			}
+
+			if (tty->update_room_in_ldisc)
+				max_space = min(left, tty->receive_room);
+			else
+				max_space = tty->receive_room;
+
+			if (count > max_space)
+				count = max_space;
 			char_buf = head->char_buf_ptr + head->read;
 			flag_buf = head->flag_buf_ptr + head->read;
 			head->read += count;
diff --git a/drivers/usb/serial/usb_wwan.c b/drivers/usb/serial/usb_wwan.c
index 366df674645..c3f741bb830 100644
--- a/drivers/usb/serial/usb_wwan.c
+++ b/drivers/usb/serial/usb_wwan.c
@@ -495,6 +495,7 @@ int usb_wwan_open(struct tty_struct *tty, struct usb_serial_port *port)
 	/* explicitly set the driver mode to raw */
 	tty->raw = 1;
 	tty->real_raw = 1;
+	tty->update_room_in_ldisc = 1;
 
 	set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
 	dbg("%s", __func__);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 6a0259d94c9..6fcafa8fe38 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -282,8 +282,10 @@ struct tty_struct {
 	struct winsize winsize;		/* termios mutex */
 	unsigned char stopped:1, hw_stopped:1, flow_stopped:1, packet:1;
 	unsigned char low_latency:1, warned:1;
+	unsigned char update_room_in_ldisc:1;
 	unsigned char ctrl_status;	/* ctrl_lock */
 	unsigned int receive_room;	/* Bytes free for queue */
+	unsigned int rr_bug;
 
 	struct tty_struct *link;
 	struct fasync_struct *fasync;