From 6d0bdc42842a8507c8218244b4ced09ca698d965 Mon Sep 17 00:00:00 2001 From: Michael Hanselmann Date: Tue, 7 Jul 2020 16:53:22 +0200 Subject: [PATCH] USB: serial: ch341: fix missing simulated-break margin On devices which do not support break signalling a break condition is simulated by sending a NUL byte at the lowest possible speed. The break condition will be 9 bit periods long (start bit and eight data bits), but the transmission itself also includes the stop bit. Add the missing safety margin of one bit which is intended to account for timing differences, and fix up the corresponding comment. Signed-off-by: Michael Hanselmann Link: https://lore.kernel.org/r/9909b288-294d-16b9-9f14-51eb79c63b6c@msgid.hansmi.ch [ johan: amend commit message ] Signed-off-by: Johan Hovold --- drivers/usb/serial/ch341.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c index 011d7953f087a..d21427aacee15 100644 --- a/drivers/usb/serial/ch341.c +++ b/drivers/usb/serial/ch341.c @@ -604,11 +604,13 @@ static void ch341_simulate_break(struct tty_struct *tty, int break_state) } /* - * Compute expected transmission duration and add a single bit - * of safety margin (the actual NUL byte transmission is 8 bits - * plus one stop bit). + * Compute expected transmission duration including safety + * margin. The original baud rate is only restored after the + * computed point in time. + * + * 11 bits = 1 start, 8 data, 1 stop, 1 margin */ - priv->break_end = jiffies + (10 * HZ / CH341_MIN_BPS); + priv->break_end = jiffies + (11 * HZ / CH341_MIN_BPS); return; } -- 2.30.2