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Subject[PATCH] pl2303: Fix mode switching regression
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>

diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.24-rc6-mm1/drivers/usb/serial/pl2303.c linux-2.6.24-rc6-mm1/drivers/usb/serial/pl2303.c
--- linux.vanilla-2.6.24-rc6-mm1/drivers/usb/serial/pl2303.c 2008-01-02 16:04:24.000000000 +0000
+++ linux-2.6.24-rc6-mm1/drivers/usb/serial/pl2303.c 2008-01-07 11:47:59.000000000 +0000
@@ -531,6 +531,13 @@
}
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);
diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.24-rc6-mm1/drivers/char/tty_ioctl.c linux-2.6.24-rc6-mm1/drivers/char/tty_ioctl.c
--- linux.vanilla-2.6.24-rc6-mm1/drivers/char/tty_ioctl.c 2008-01-02 16:04:19.000000000 +0000
+++ linux-2.6.24-rc6-mm1/drivers/char/tty_ioctl.c 2008-01-07 11:43:39.000000000 +0000
@@ -360,6 +360,25 @@
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
* @new_termios: desired new value
diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.24-rc6-mm1/include/linux/tty.h linux-2.6.24-rc6-mm1/include/linux/tty.h
--- linux.vanilla-2.6.24-rc6-mm1/include/linux/tty.h 2008-01-02 16:04:25.000000000 +0000
+++ linux-2.6.24-rc6-mm1/include/linux/tty.h 2008-01-07 11:43:19.000000000 +0000
@@ -312,6 +312,7 @@
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 *);

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