From 1796a228762cd0b86e14d6d4a3de9ecfe65b3b8d Mon Sep 17 00:00:00 2001 From: Greg Kroah-Hartman Date: Fri, 1 Nov 2013 09:19:45 -0700 Subject: [PATCH] Revert "usb: pl2303: fix+improve the divsor based baud rate encoding method" MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Cc: Frank Schäfer Acked-by: Johan Hovold Signed-off-by: Greg Kroah-Hartman --- drivers/usb/serial/pl2303.c | 62 ++++++------------------------------- 1 file 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 - * - fixes, improvements and documentation for the baud rate encoding methods - * Copyright (C) 2013 Reinhard Max - * - 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 */ -- 2.20.1