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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
index e02d592..d4b6d64 100644
--- a/drivers/char/tty_ioctl.c
+++ b/drivers/char/tty_ioctl.c
@@ -365,6 +365,25 @@
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 --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index cf8add9..0da1df9 100644
--- a/drivers/usb/serial/pl2303.c
+++ b/drivers/usb/serial/pl2303.c
@@ -483,6 +483,13 @@
}
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 --git a/include/linux/tty.h b/include/linux/tty.h
index c555f54..defd2ab 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -319,6 +319,7 @@
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 *);