USB: PL2303: correctly handle baudrates above 115200

commit 8d48fdf6 upstream.

PL2303: correctly handle baudrates above 115200
Signed-off-by: Michal Sroczynski <msroczyn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/pl2303.c

@@ -617,10 +617,28 @@ static void pl2303_set_termios(struct tty_struct *tty,
 				baud = 6000000;
 		}
 		dbg("%s - baud set = %d", __func__, baud);
-		buf[0] = baud & 0xff;
-		buf[1] = (baud >> 8) & 0xff;
-		buf[2] = (baud >> 16) & 0xff;
-		buf[3] = (baud >> 24) & 0xff;
+		if (baud <= 115200) {
+			buf[0] = baud & 0xff;
+			buf[1] = (baud >> 8) & 0xff;
+			buf[2] = (baud >> 16) & 0xff;
+			buf[3] = (baud >> 24) & 0xff;
+		} else {
+			/* apparently the formula for higher speeds is:
+			 * baudrate = 12M * 32 / (2^buf[1]) / buf[0]
+			 */
+			unsigned tmp = 12*1000*1000*32 / baud;
+			buf[3] = 0x80;
+			buf[2] = 0;
+			buf[1] = (tmp >= 256);
+			while (tmp >= 256) {
+				tmp >>= 2;
+				buf[1] <<= 1;
+			}
+			if (tmp > 256) {
+				tmp %= 256;
+			}
+			buf[0] = tmp;
+		}
 	}
 
 	/* For reference buf[4]=0 is 1 stop bits */