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>
diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index b93b3b3..2448201 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 @@
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 */
