Commit 1796a228 authored by Greg Kroah-Hartman's avatar Greg Kroah-Hartman

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

This reverts commit 57ce61aa.

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: default avatarMika Westerberg <mika.westerberg@linux.intel.com>
Cc: Frank Schäfer <fschaefer.oss@googlemail.com>
Acked-by: default avatarJohan Hovold <jhovold@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 7e12a6fc
......@@ -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
*/
/* 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.
* Apparently the formula for higher speeds is:
* baudrate = 12M * 32 / (2^buf[1]) / buf[0]
*/
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 */
......
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