Revert "usb: pl2303: fix+improve the divsor based baud rate encoding method"

This reverts commit 57ce61aad748ceaa08c859da04043ad7dae7c15e.

Revert all of the pl2303 changes that went into 3.12-rc1 and -rc2 as
they cause regressions on some versions of the chip.  This will all be
revisited for later kernel versions when we can figure out how to handle
this in a way that does not break working devices.

Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Frank Schäfer <fschaefer.oss@googlemail.com>
Acked-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 10 insertions, 52 deletions

diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index b93b3b30dec5..244820193e10 100644
--- a/drivers/usb/serial/pl2303.c
+++ b/drivers/usb/serial/pl2303.c
@@ -4,11 +4,6 @@
  * Copyright (C) 2001-2007 Greg Kroah-Hartman (greg@kroah.com)
  * Copyright (C) 2003 IBM Corp.
  *
- * Copyright (C) 2009, 2013 Frank Schäfer <fschaefer.oss@googlemail.com>
- *  - fixes, improvements and documentation for the baud rate encoding methods
- * Copyright (C) 2013 Reinhard Max <max@suse.de>
- *  - fixes and improvements for the divisor based baud rate encoding method
- *
  * Original driver for 2.2.x by anonymous
  *
  *      This program is free software; you can redistribute it and/or
@@ -315,58 +310,21 @@ static void pl2303_encode_baudrate(struct tty_struct *tty,
                 put_unaligned_le32(baud, buf);
         } else {
                 /*
-                 * Divisor based baud rate encoding method
-                 *
                  * NOTE: it's not clear if the type_0/1 chips
                  * support this method
                  *
-                 * divisor = 12MHz * 32 / baudrate = 2^A * B
-                 *
-                 * with
-                 *
-                 * A = buf[1] & 0x0e
-                 * B = buf[0]  +  (buf[1] & 0x01) << 8
-                 *
-                 * Special cases:
-                 * => 8 < B < 16: device seems to work not properly
-                 * => B <= 8: device uses the max. value B = 512 instead
+                 * Apparently the formula for higher speeds is:
+                 * baudrate = 12M * 32 / (2^buf[1]) / buf[0]
                  */
-
-                /* Determine factors A and B */
-                unsigned int A = 0;
-                unsigned int B = 12000000 * 32 / baud;  /* 12MHz */
-                B <<= 1; /* Add one bit for rounding */
-                while (B > (512 << 1) && A <= 14) {
-                        A += 2;
-                        B >>= 2;
-                }
-                if (A > 14) { /* max. divisor = min. baudrate reached */
-                        A = 14;
-                        B = 512;
-                        /* => ~45.78 baud */
-                } else {
-                        B = (B + 1) >> 1; /* Round the last bit */
-                }
-                /* Handle special cases */
-                if (B == 512)
-                        B = 0; /* also: 1 to 8 */
-                else if (B < 16)
-                        /*
-                         * NOTE: With the current algorithm this happens
-                         * only for A=0 and means that the min. divisor
-                         * (respectively: the max. baudrate) is reached.
-                         */
-                        B = 16;         /* => 24 MBaud */
-                /* Encode the baud rate */
-                buf[3] = 0x80;     /* Select divisor encoding method */
+                unsigned tmp = 12000000 * 32 / baud;
+                buf[3] = 0x80;
                 buf[2] = 0;
-                buf[1] = (A & 0x0e);            /* A */
-                buf[1] |= ((B & 0x100) >> 8);   /* MSB of B */
-                buf[0] = B & 0xff;              /* 8 LSBs of B */
-                /* Calculate the actual/resulting baud rate */
-                if (B <= 8)
-                        B = 512;
-                baud = 12000000 * 32 / ((1 << A) * B);
+                buf[1] = (tmp >= 256);
+                while (tmp >= 256) {
+                        tmp >>= 2;
+                        buf[1] <<= 1;
+                }
+                buf[0] = tmp;
         }
 
         /* Save resulting baud rate */