USB: pl2303: use divisors for unsupported baud rates

Use direct method for supported baud rates, otherwise use divisors.
Limit baud rate to 12 Mbaud with HX type.

This change has been tested to work with PL-2303HX at 115200, 500000,
1000000, 2000000, 2500000, 3000000 and 4000000 baud rates.

Signed-off-by: Lauri Hintsala <lauri.hintsala@bluegiga.com>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/pl2303.c

@@ -162,6 +162,9 @@ static const struct pl2303_type_data pl2303_type_data[TYPE_COUNT] = {
 		.max_baud_rate =	1228800,
 		.quirks =		PL2303_QUIRK_LEGACY,
 	},
+	[TYPE_HX] = {
+		.max_baud_rate =	12000000,
+	},
 };
 
 static int pl2303_vendor_read(struct usb_serial *serial, u16 value,
@@ -395,16 +398,14 @@ static void pl2303_encode_baud_rate(struct tty_struct *tty,
 	if (spriv->type->max_baud_rate)
 		baud = min_t(speed_t, baud, spriv->type->max_baud_rate);
 	/*
-	 * Set baud rate to nearest supported value.
-	 *
-	 * NOTE: Baud rate 500k can only be set using divisors.
+	 * Use direct method for supported baud rates, otherwise use divisors.
 	 */
 	baud_sup = pl2303_get_supported_baud_rate(baud);
 
-	if (baud == 500000)
-		baud = pl2303_encode_baud_rate_divisor(buf, baud);
+	if (baud == baud_sup)
+		baud = pl2303_encode_baud_rate_direct(buf, baud);
 	else
-		baud = pl2303_encode_baud_rate_direct(buf, baud_sup);
+		baud = pl2303_encode_baud_rate_divisor(buf, baud);
 
 	/* Save resulting baud rate */
 	tty_encode_baud_rate(tty, baud, baud);