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Subject[v2.6.34-stable 137/165] USB: Fix Corruption issue in USB ftdi driver ftdi_sio.c
Date
From: Andrew Worsley <amworsley@gmail.com>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
If you see a problem with using this for longterm, please comment.
-------------------

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>
----

I had a brief run with strace on the getty and it was doing ioctl()s on
each call but it didn't look relavant to the problem. I think the issue is
that XON/XOFF flow control was being implmented via hardware - for the ixoff
to allow the user to use XON/XOFF to control output. Unfortunately it would
send 3 Control URBs updating all of the settings after each piece of input

I am trying to work around the issue of gmail messing with the tab/spacing
by submitting via SMTP via gmail which I believe should fix the issue.

The patch is against v3.2-rc2 and compiles - but no additional testing in
this kernel has been done.

Thanks

Andrew

Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
drivers/usb/serial/ftdi_sio.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 24dc63c..7367f4b 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -2332,13 +2332,19 @@ static void ftdi_set_termios(struct tty_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;
@@ -2379,6 +2385,7 @@ static void ftdi_set_termios(struct tty_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),
@@ -2406,6 +2413,7 @@ static void ftdi_set_termios(struct tty_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,
--
1.7.12.rc2


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