[38/53] USB: Fix Corruption issue in USB ftdi driver ftdi_sio.c

Greg KH
2011-11-23T00:43:12Z

From: Andrew Worsley <amworsley@gmail.com>

commit b1ffb4c851f185e9051ba837c16d9b84ef688d26 upstream.

Fix for ftdi_set_termios() glitching output

ftdi_set_termios() is constantly setting the baud rate, data bits and parity
unnecessarily on every call, . When called while characters are being
transmitted can cause the FTDI chip to corrupt the serial port bit stream
output by stalling the output half a bit during the output of a character.
Simple fix by skipping this setting if the baud rate/data bits/parity are
unchanged.

Signed-off-by: Andrew Worsley <amworsley@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/usb/serial/ftdi_sio.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -2080,13 +2080,19 @@ static void ftdi_set_termios(struct tty_

cflag = termios->c_cflag;

- /* FIXME -For this cut I don't care if the line is really changing or
- not - so just do the change regardless - should be able to
- compare old_termios and tty->termios */
+ if (old_termios->c_cflag == termios->c_cflag
+ && old_termios->c_ispeed == termios->c_ispeed
+ && old_termios->c_ospeed == termios->c_ospeed)
+ goto no_c_cflag_changes;
+
/* NOTE These routines can get interrupted by
ftdi_sio_read_bulk_callback - need to examine what this means -
don't see any problems yet */

+ if ((old_termios->c_cflag & (CSIZE|PARODD|PARENB|CMSPAR|CSTOPB)) ==
+ (termios->c_cflag & (CSIZE|PARODD|PARENB|CMSPAR|CSTOPB)))
+ goto no_data_parity_stop_changes;
+
/* Set number of data bits, parity, stop bits */

urb_value = 0;
@@ -2127,6 +2133,7 @@ static void ftdi_set_termios(struct tty_
}

/* Now do the baudrate */
+no_data_parity_stop_changes:
if ((cflag & CBAUD) == B0) {
/* Disable flow control */
if (usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
@@ -2154,6 +2161,7 @@ static void ftdi_set_termios(struct tty_

/* Set flow control */
/* Note device also supports DTR/CD (ugh) and Xon/Xoff in hardware */
+no_c_cflag_changes:
if (cflag & CRTSCTS) {
dbg("%s Setting to CRTSCTS flow control", __func__);
if (usb_control_msg(dev,