Staging: quatech_usb2: Improvements to set_termios method

This patch implements several improvements to the set_termios method
suggested by Alan Cox:
* Correct check for whether any changes are being requested.
* Inform callers that mark/space parity isn't supported by always
clearing the bit.
* Pass back the actual used baud rate in case it doesn't match what was
requested.

Remaining known issues are that IXANY flow control is not supported, but
we don't tell the caller that, and input and output XON/XOFF flow
control are either both on or both off, but we don't indicate that back
to the caller either.

Signed-off-by: Richard Ash <richard@audacityteam.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/quatech_usb2/TODO

@@ -0,0 +1,8 @@
+Incomplete list of things that this driver does not yet implement completely or
+at all. some of these may not be possible to implement because the hardware
+support does not exist. Others may be possible, but the magic control codes to
+make them happen are unknown, and some may just need the driver support to
+implement them writing.
+
+* Mark/Space parity is not implemented (reported back correctly)
+* IXANY flow control mode is not implemented (flag ignored completely)

drivers/staging/quatech_usb2/quatech_usb2.c

@@ -83,8 +83,8 @@ static int debug;
 #define QT2_SERIAL_6_DATA	0x01
 #define QT2_SERIAL_5_DATA	0x00
 
-#define QT2_SERIAL_ODD_PARITY	0X08
-#define QT2_SERIAL_EVEN_PARITY	0X18
+#define QT2_SERIAL_ODD_PARITY	0x08
+#define QT2_SERIAL_EVEN_PARITY	0x18
 #define QT2_SERIAL_TWO_STOPB	0x04
 #define QT2_SERIAL_ONE_STOPB	0x00
 
@@ -978,14 +978,8 @@ static void qt2_set_termios(struct tty_struct *tty,
 
 	UartNumber = port->number;
 
-	if (old_termios) {
-		if ((tty->termios->c_cflag == old_termios->c_cflag) &&
-			(RELEVANT_IFLAG(tty->termios->c_iflag) ==
-			RELEVANT_IFLAG(old_termios->c_iflag))) {
-			dbg("%s(): Nothing to change", __func__);
-			return;
-		}
-	}
+	if (old_termios && !tty_termios_hw_change(old_termios, tty->termios))
+		return;
 
 	switch (tty->termios->c_cflag) {
 	case CS5:
@@ -1010,12 +1004,21 @@ static void qt2_set_termios(struct tty_struct *tty,
 		else
 			LCR_change_to |= QT2_SERIAL_EVEN_PARITY;
 	}
+	/* Because LCR_change_to is initialised to zero, we don't have to worry
+	 * about the case where PARENB is not set or clearing bits, because by
+	 * default all of them are cleared, turning parity off.
+	 * as we don't support mark/space parity, we should clear the
+	 * mark/space parity bit in c_cflag, so the caller can tell we have
+	 * ignored the request */
+	tty->termios->c_cflag &= ~CMSPAR;
+
 	if (tty->termios->c_cflag & CSTOPB)
 		LCR_change_to |= QT2_SERIAL_TWO_STOPB;
 	else
 		LCR_change_to |= QT2_SERIAL_ONE_STOPB;
 
-	/* Thats the LCR stuff, go ahead and set it */
+	/* Thats the LCR stuff, next we need to work out the divisor as the
+	 * LCR and the divisor are set together */
 	baud = tty_get_baud_rate(tty);
 	if (!baud) {
 		/* pick a default, any default... */
@@ -1036,6 +1039,11 @@ static void qt2_set_termios(struct tty_struct *tty,
 	if (status < 0)	{
 		dbg("qt2_boxsetuart() failed");
 		return;
+	} else {
+		/* now encode the baud rate we actually set, which may be
+		 * different to the request */
+		baud = QT2_MAX_BAUD_RATE / divisor;
+		tty_encode_baud_rate(tty, baud, baud);
 	}
 
 	/* Now determine flow control */