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

drivers/usb/serial/pl2303.c

+10 −52
Original line number Diff line number Diff line
@@ -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 */

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