serial: sh-sci: Add calculation recive margin for HSCIF

When the error of the same bit rate is detected, we will need to select
the recive margin is large. Current code holds the minimum error, it does
not have to check the recive margin. This adds this calculation.
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -1776,13 +1776,30 @@ static unsigned int sci_scbrr_calc(struct sci_port *s, unsigned int bps,
 	return ((freq + 16 * bps) / (32 * bps) - 1);
 }
 
+/* calculate frame length from SMR */
+static int sci_baud_calc_frame_len(unsigned int smr_val)
+{
+	int len = 10;
+
+	if (smr_val & SCSMR_CHR)
+		len--;
+	if (smr_val & SCSMR_PE)
+		len++;
+	if (smr_val & SCSMR_STOP)
+		len++;
+
+	return len;
+}
+
+
 /* calculate sample rate, BRR, and clock select for HSCIF */
 static void sci_baud_calc_hscif(unsigned int bps, unsigned long freq,
 				int *brr, unsigned int *srr,
-				unsigned int *cks)
+				unsigned int *cks, int frame_len)
 {
-	int sr, c, br, err;
+	int sr, c, br, err, recv_margin;
 	int min_err = 1000; /* 100% */
+	int recv_max_margin = 0;
 
 	/* Find the combination of sample rate and clock select with the
 	   smallest deviation from the desired baud rate. */
@@ -1795,12 +1812,35 @@ static void sci_baud_calc_hscif(unsigned int bps, unsigned long freq,
 			err = DIV_ROUND_CLOSEST(freq, ((br + 1) * bps * sr *
 					       (1 << (2 * c + 1)) / 1000)) -
 					       1000;
+			if (err < 0)
+				continue;
+
+			/* Calc recv margin
+			 * M: Receive margin (%)
+			 * N: Ratio of bit rate to clock (N = sampling rate)
+			 * D: Clock duty (D = 0 to 1.0)
+			 * L: Frame length (L = 9 to 12)
+			 * F: Absolute value of clock frequency deviation
+			 *
+			 *  M = |(0.5 - 1 / 2 * N) - ((L - 0.5) * F) -
+			 *      (|D - 0.5| / N * (1 + F))|
+			 *  NOTE: Usually, treat D for 0.5, F is 0 by this
+			 *        calculation.
+			 */
+			recv_margin = abs((500 -
+					DIV_ROUND_CLOSEST(1000, sr << 1)) / 10);
 			if (min_err > err) {
 				min_err = err;
-				*brr = br;
-				*srr = sr - 1;
-				*cks = c;
-			}
+				recv_max_margin = recv_margin;
+			} else if ((min_err == err) &&
+				   (recv_margin > recv_max_margin))
+				recv_max_margin = recv_margin;
+			else
+				continue;
+
+			*brr = br;
+			*srr = sr - 1;
+			*cks = c;
 		}
 	}
 
@@ -1834,10 +1874,19 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
 {
 	struct sci_port *s = to_sci_port(port);
 	struct plat_sci_reg *reg;
-	unsigned int baud, smr_val, max_baud, cks = 0;
+	unsigned int baud, smr_val = 0, max_baud, cks = 0;
 	int t = -1;
 	unsigned int srr = 15;
 
+	if ((termios->c_cflag & CSIZE) == CS7)
+		smr_val |= SCSMR_CHR;
+	if (termios->c_cflag & PARENB)
+		smr_val |= SCSMR_PE;
+	if (termios->c_cflag & PARODD)
+		smr_val |= SCSMR_PE | SCSMR_ODD;
+	if (termios->c_cflag & CSTOPB)
+		smr_val |= SCSMR_STOP;
+
 	/*
 	 * earlyprintk comes here early on with port->uartclk set to zero.
 	 * the clock framework is not up and running at this point so here
@@ -1851,8 +1900,9 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
 	baud = uart_get_baud_rate(port, termios, old, 0, max_baud);
 	if (likely(baud && port->uartclk)) {
 		if (s->cfg->type == PORT_HSCIF) {
+			int frame_len = sci_baud_calc_frame_len(smr_val);
 			sci_baud_calc_hscif(baud, port->uartclk, &t, &srr,
-					    &cks);
+					    &cks, frame_len);
 		} else {
 			t = sci_scbrr_calc(s, baud, port->uartclk);
 			for (cks = 0; t >= 256 && cks <= 3; cks++)
@@ -1864,16 +1914,7 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
 
 	sci_reset(port);
 
-	smr_val = serial_port_in(port, SCSMR) & 3;
-
-	if ((termios->c_cflag & CSIZE) == CS7)
-		smr_val |= SCSMR_CHR;
-	if (termios->c_cflag & PARENB)
-		smr_val |= SCSMR_PE;
-	if (termios->c_cflag & PARODD)
-		smr_val |= SCSMR_PE | SCSMR_ODD;
-	if (termios->c_cflag & CSTOPB)
-		smr_val |= SCSMR_STOP;
+	smr_val |= serial_port_in(port, SCSMR) & 3;
 
 	uart_update_timeout(port, termios->c_cflag, baud);