usb: pl2303: do not round to the next nearest standard baud rate for …

…the divisor based baud rate encoding method

In opposition to the direct baud rate encoding method, the divisor
based method is not limited to a fixed set of standard baud rates.
Hence, there is no need to round to the next nearest standard value.

Reported-by: Mastro Gippo <gipmad@gmail.com>
Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Reinhard Max <max@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/pl2303.c

@@ -273,44 +273,46 @@ static void pl2303_encode_baudrate(struct tty_struct *tty,
 					struct usb_serial_port *port,
 					u8 buf[4])
 {
-	const int baud_sup[] = { 75, 150, 300, 600, 1200, 1800, 2400, 3600,
-	                         4800, 7200, 9600, 14400, 19200, 28800, 38400,
-	                         57600, 115200, 230400, 460800, 500000, 614400,
-	                         921600, 1228800, 2457600, 3000000, 6000000 };
-
 	struct usb_serial *serial = port->serial;
 	struct pl2303_serial_private *spriv = usb_get_serial_data(serial);
 	int baud;
-	int i;
 
-	/*
-	 * NOTE: Only the values defined in baud_sup are supported!
-	 *       => if unsupported values are set, the PL2303 seems to use
-	 *          9600 baud (at least my PL2303X always does)
-	 */
 	baud = tty_get_baud_rate(tty);
 	dev_dbg(&port->dev, "baud requested = %d\n", baud);
 	if (!baud)
 		return;
 
-	/* Set baudrate to nearest supported value */
-	for (i = 0; i < ARRAY_SIZE(baud_sup); ++i) {
-		if (baud_sup[i] > baud)
-			break;
-	}
+	if (spriv->type != HX || baud <= 115200) {
+		/*
+		 * NOTE: Only the values defined in baud_sup are supported !
+		 *       => if unsupported values are set, the PL2303 seems to
+		 *	    use 9600 baud (at least my PL2303X always does)
+		 */
+		const int baud_sup[] = { 75, 150, 300, 600, 1200, 1800, 2400,
+					 3600, 4800, 7200, 9600, 14400, 19200,
+					 28800, 38400, 57600, 115200, 230400,
+					 460800, 500000, 614400, 921600,
+					 1228800, 2457600, 3000000, 6000000 };
+		int i;
+
+		/* Set baudrate to nearest supported value */
+		for (i = 0; i < ARRAY_SIZE(baud_sup); ++i) {
+			if (baud_sup[i] > baud)
+				break;
+		}
 
-	if (i == ARRAY_SIZE(baud_sup))
-		baud = baud_sup[i - 1];
-	else if (i > 0 && (baud_sup[i] - baud) > (baud - baud_sup[i - 1]))
-		baud = baud_sup[i - 1];
-	else
-		baud = baud_sup[i];
+		if (i == ARRAY_SIZE(baud_sup))
+			baud = baud_sup[i - 1];
+		else if (i > 0
+			     && (baud_sup[i] - baud) > (baud - baud_sup[i - 1]))
+			baud = baud_sup[i - 1];
+		else
+			baud = baud_sup[i];
 
-	/* type_0, type_1 only support up to 1228800 baud */
-	if (spriv->type != HX)
-		baud = min_t(int, baud, 1228800);
+		/* type_0, type_1 only support up to 1228800 baud */
+		if (spriv->type != HX)
+			baud = min_t(int, baud, 1228800);
 
-	if (spriv->type != HX || baud <= 115200) {
 		/* Direct (standard) baud rate encoding method */
 		put_unaligned_le32(baud, buf);
 	} else {
@@ -331,10 +333,17 @@ static void pl2303_encode_baudrate(struct tty_struct *tty,
 		 * => 8 < B < 16: device seems to work not properly
 		 * => B <= 8: device uses the max. value B = 512 instead
 		 */
+		unsigned int A, B;
 
+		/* Respect the specified baud rate limits */
+		baud = max_t(int, baud, 75);
+		if (spriv->type == HX)
+			baud = min_t(int, baud, 6000000);
+		else
+			baud = min_t(int, baud, 1228800);
 		/* Determine factors A and B */
-		unsigned int A = 0;
-		unsigned int B = 12000000 * 32 / baud;  /* 12MHz */
+		A = 0;
+		B = 12000000 * 32 / baud;  /* 12MHz */
 		B <<= 1; /* Add one bit for rounding */
 		while (B > (512 << 1) && A <= 14) {
 			A += 2;