Commit ace96569 authored Apr 01, 2019 by Geert Uytterhoeven Committed by Greg Kroah-Hartman Apr 16, 2019

serial: sh-sci: Fix HSCIF RX sampling point calculation



There are several issues with the formula used for calculating the
deviation from the intended rate:
  1. While min_err and last_stop are signed, srr and baud are unsigned.
     Hence the signed values are promoted to unsigned, which will lead
     to a bogus value of deviation if min_err is negative,
  2. Srr is the register field value, which is one less than the actual
     sampling rate factor,
  3. The divisions do not use rounding.

Fix this by casting unsigned variables to int, adding one to srr, and
using a single DIV_ROUND_CLOSEST().

Fixes: 63ba1e00 ("serial: sh-sci: Support for HSCIF RX sampling point adjustment")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 79a3aaa7

drivers/tty/serial/sh-sci.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -2512,7 +2512,9 @@ static void sci_set_termios(struct uart_port port, struct ktermios termios,
		* center of the last stop bit in sampling clocks.
		*/
		int last_stop = bits * 2 - 1;
		int deviation = min_err * srr * last_stop / 2 / baud;
		int deviation = DIV_ROUND_CLOSEST(min_err * last_stop *
		(int)(srr + 1),
		2 * (int)baud);

		if (abs(deviation) >= 2) {
		/* At least two sampling clocks off at the