USB: PL2303: correctly handle baudrates above 115200

PL2303: correctly handle baudrates above 115200

Signed-off-by: Michal Sroczynski <msroczyn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index 30461fcc2206ea6182193f50f9b56bce0d5a7928..ee28115aa9b47a37d7901c4daadbfc556d588eea 100644 (file)
--- a/drivers/usb/serial/pl2303.c
+++ b/drivers/usb/serial/pl2303.c
@@ -342,10 +342,28 @@ 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 */