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

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;