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pl2303: Fix mode switching regression

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Cleaning out all the incorrect 'no change made' checks for termios
settings showed up a problem with the PL2303. The hardware here seems to
lose sync and bits if you tell it to make no changes. This shows up with
a real world application.

To fix this the driver check for meaningful hardware changes is restored
but doing the tests correctly and as a tty layer function so it doesn't
get duplicated wrongly everywhere if other drivers turn out to need it.

Signed-off-by: Alan Cox <alan@redhat.com>
Tested-by: Mirko Parthey <mirko.parthey@informatik.tu-chemnitz.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Alan Cox 2008-01-08 14:55:51 +00:00 committed by Linus Torvalds
parent cf05946250
commit bf5e5834bf
3 changed files with 27 additions and 0 deletions
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19
drivers/char/tty_ioctl.c
View file

@ -364,6 +364,25 @@ void tty_termios_copy_hw(struct ktermios *new, struct ktermios *old)
EXPORT_SYMBOL(tty_termios_copy_hw);
/**
* tty_termios_hw_change - check for setting change
* @a: termios
* @b: termios to compare
*
* Check if any of the bits that affect a dumb device have changed
* between the two termios structures, or a speed change is needed.
*/
int tty_termios_hw_change(struct ktermios *a, struct ktermios *b)
{
if (a->c_ispeed != b->c_ispeed || a->c_ospeed != b->c_ospeed)
return 1;
if ((a->c_cflag ^ b->c_cflag) & ~(HUPCL | CREAD | CLOCAL))
return 1;
return 0;
}
EXPORT_SYMBOL(tty_termios_hw_change);
/**
* change_termios - update termios values
* @tty: tty to update

7
drivers/usb/serial/pl2303.c
View file

@ -483,6 +483,13 @@ static void pl2303_set_termios(struct usb_serial_port *port,
}
spin_unlock_irqrestore(&priv->lock, flags);
/* The PL2303 is reported to lose bytes if you change
serial settings even to the same values as before. Thus
we actually need to filter in this specific case */
if (!tty_termios_hw_change(port->tty->termios, old_termios))
return;
cflag = port->tty->termios->c_cflag;
buf = kzalloc(7, GFP_KERNEL);

1
include/linux/tty.h
View file

@ -319,6 +319,7 @@ extern speed_t tty_termios_input_baud_rate(struct ktermios *termios);
extern void tty_termios_encode_baud_rate(struct ktermios *termios, speed_t ibaud, speed_t obaud);
extern void tty_encode_baud_rate(struct tty_struct *tty, speed_t ibaud, speed_t obaud);
extern void tty_termios_copy_hw(struct ktermios *new, struct ktermios *old);
extern int tty_termios_hw_change(struct ktermios *a, struct ktermios *b);
extern struct tty_ldisc *tty_ldisc_ref(struct tty_struct *);
extern void tty_ldisc_deref(struct tty_ldisc *);