diff options
Diffstat (limited to 'drivers/usb/serial/pl2303.c')
| -rw-r--r-- | drivers/usb/serial/pl2303.c | 62 |
1 files changed, 10 insertions, 52 deletions
diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c index b93b3b30dec..244820193e1 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 */ |