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USB: Fix Corruption issue in USB ftdi driver ftdi_sio.c

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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>
Cc: stable <stable@vger.kernel.org>
----

  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>
This commit is contained in:
Andrew Worsley 2011-11-18 23:13:33 +11:00 committed by Greg Kroah-Hartman
parent 4aa3648c71
commit b1ffb4c851
1 changed files with 11 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
drivers/usb/serial/ftdi_sio.c
View File

@ -2104,13 +2104,19 @@ 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;
@ -2151,6 +2157,7 @@ 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),
@ -2178,6 +2185,7 @@ 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,