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>

1 files changed, 22 insertions, 4 deletions

diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index 30461fcc220..ee28115aa9b 100644
--- 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 */