@@ -361,21 +361,38 @@ static speed_t pl2303_encode_baud_rate_direct(unsigned char buf[4],
static speed_t pl2303_encode_baud_rate_divisor(unsigned char buf[4],
speed_t baud)
{
- unsigned int tmp;
+ unsigned int baseline, mantissa, exponent;
/*
* Apparently the formula is:
- * baudrate = 12M * 32 / (2^buf[1]) / buf[0]
+ * baudrate = 12M * 32 / (mantissa * 4^exponent)
+ * where
+ * mantissa = buf[8:0]
+ * exponent = buf[11:9]
*/
- tmp = 12000000 * 32 / baud;
+ baseline = 12000000 * 32;
+ mantissa = baseline / baud;
+ if (mantissa == 0)
+ mantissa = 1; /* Avoid dividing by zero if baud > 32*12M. */
+ exponent = 0;
+ while (mantissa >= 512) {
+ if (exponent < 7) {
+ mantissa >>= 2; /* divide by 4 */
+ exponent++;
+ } else {
+ /* Exponent is maxed. Trim mantissa and leave. */
+ mantissa = 511;
+ break;
+ }
+ }
+
buf[3] = 0x80;
buf[2] = 0;
- buf[1] = (tmp >= 256);
- while (tmp >= 256) {
- tmp >>= 2;
- buf[1] <<= 1;
- }
- buf[0] = tmp;
+ buf[1] = exponent << 1 | mantissa >> 8;
+ buf[0] = mantissa & 0xff;
+
+ /* Calculate and return the exact baud rate. */
+ baud = (baseline / mantissa) >> (exponent << 1);
return baud;
}
This is a note to let you know that I have just added a patch titled USB: pl2303: fix baud-rate divisor calculations to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue This patch is scheduled to be released in version 3.19.8-ckt8. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.19.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From 73de4b351638bf08d13968dd73a8524c0dbc35cf Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Micha=C5=82=20Pecio?= <michal.pecio@gmail.com> Date: Sun, 26 Jul 2015 11:14:34 +0200 Subject: USB: pl2303: fix baud-rate divisor calculations commit 49bda21266fdf195142e8b5dea057f09e96ada9f upstream. This commit fixes the following issues: 1. The 9th bit of buf was believed to be the LSB of divisor's exponent, but the hardware interprets it as MSB (9th bit) of the mantissa. The exponent is actually one bit shorter and applies to base 4, not 2 as previously believed. 2. Loop iterations doubled the exponent instead of incrementing. 3. The exponent wasn't checked for overflow. 4. The function returned requested rate instead of actual rate. Due to issue #2, the old code deviated from the wrong formula described in #1 and actually yielded correct rates when divisor was lower than 4096 by using exponents of 0, 2 or 4 base-2, interpreted as 0, 1, 2 base-4 with the 9th mantissa bit clear. However, at 93.75 kbaud or less the rate turned out too slow due to #2 or too fast due to #2 and #3. I tested this patch by sending and validating 0x00,0x01,..,0xff to an FTDI dongle at 234, 987, 2401, 9601, 31415, 115199, 250k, 500k, 750k, 1M, 1.5M, 3M+1 baud. All rates passed. I also used pv to check speed at some rates unsupported by FTDI: 45 (the lowest possible), 2M, 4M, 5M and 6M-1. Looked sane. Signed-off-by: Michal Pecio <michal.pecio@gmail.com> Fixes: 399aa9a75ad3 ("USB: pl2303: use divisors for unsupported baud rates") [johan: update summary ] Signed-off-by: Johan Hovold <johan@kernel.org> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- drivers/usb/serial/pl2303.c | 35 ++++++++++++++++++++++++++--------- 1 file changed, 26 insertions(+), 9 deletions(-) -- 1.9.1