[PATCH 2/2] serial: sccnxp: Allow to use non-standard baud rates

[Alexander Shiyan <shc_work@xxxxxxx>]

This patch adds support for the use of non-standard baud rates.
For these purposes, we use the built-in timer/counter.

Signed-off-by: Alexander Shiyan <shc_work@xxxxxxx>
---
 drivers/tty/serial/sccnxp.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/sccnxp.c b/drivers/tty/serial/sccnxp.c
index c0a68eee4479..68a24a14f6b7 100644
--- a/drivers/tty/serial/sccnxp.c
+++ b/drivers/tty/serial/sccnxp.c
@@ -48,7 +48,6 @@
 #	define MR2_STOP1		(7 << 0)
 #	define MR2_STOP2		(0xf << 0)
 #define SCCNXP_SR_REG			(0x01)
-#define SCCNXP_CSR_REG			SCCNXP_SR_REG
 #	define SR_RXRDY			(1 << 0)
 #	define SR_FULL			(1 << 1)
 #	define SR_TXRDY			(1 << 2)
@@ -57,6 +56,8 @@
 #	define SR_PE			(1 << 5)
 #	define SR_FE			(1 << 6)
 #	define SR_BRK			(1 << 7)
+#define SCCNXP_CSR_REG			(SCCNXP_SR_REG)
+#	define CSR_TIMER_MODE		(0x0d)
 #define SCCNXP_CR_REG			(0x02)
 #	define CR_RX_ENABLE		(1 << 0)
 #	define CR_RX_DISABLE		(1 << 1)
@@ -83,9 +84,12 @@
 #	define IMR_RXRDY		(1 << 1)
 #	define ISR_TXRDY(x)		(1 << ((x * 4) + 0))
 #	define ISR_RXRDY(x)		(1 << ((x * 4) + 1))
+#define SCCNXP_CTPU_REG			(0x06)
+#define SCCNXP_CTPL_REG			(0x07)
 #define SCCNXP_IPR_REG			(0x0d)
 #define SCCNXP_OPCR_REG			SCCNXP_IPR_REG
 #define SCCNXP_SOP_REG			(0x0e)
+#define SCCNXP_START_COUNTER_REG	SCCNXP_SOP_REG
 #define SCCNXP_ROP_REG			(0x0f)
 
 /* Route helpers */
@@ -255,7 +259,7 @@ static int sccnxp_update_best_err(int a, int b, int *besterr)
 {
 	int err = abs(a - b);
 
-	if ((*besterr < 0) || (*besterr > err)) {
+	if (*besterr > err) {
 		*besterr = err;
 		return 0;
 	}
@@ -303,10 +307,22 @@ static const struct {
 static int sccnxp_set_baud(struct uart_port *port, int baud)
 {
 	struct sccnxp_port *s = dev_get_drvdata(port->dev);
-	int div_std, tmp_baud, bestbaud = baud, besterr = -1;
+	int div_std, tmp_baud, bestbaud = INT_MAX, besterr = INT_MAX;
 	struct sccnxp_chip *chip = s->chip;
 	u8 i, acr = 0, csr = 0, mr0 = 0;
 
+	/* Find divisor to load to the timer preset registers */
+	div_std = DIV_ROUND_CLOSEST(port->uartclk, 2 * 16 * baud);
+	if ((div_std >= 2) && (div_std <= 0xffff)) {
+		bestbaud = DIV_ROUND_CLOSEST(port->uartclk, 2 * 16 * div_std);
+		sccnxp_update_best_err(baud, bestbaud, &besterr);
+		csr = CSR_TIMER_MODE;
+		sccnxp_port_write(port, SCCNXP_CTPU_REG, div_std >> 8);
+		sccnxp_port_write(port, SCCNXP_CTPL_REG, div_std);
+		/* Issue start timer/counter command */
+		sccnxp_port_read(port, SCCNXP_START_COUNTER_REG);
+	}
+
 	/* Find best baud from table */
 	for (i = 0; baud_std[i].baud && besterr; i++) {
 		if (baud_std[i].mr0 && !(chip->flags & SCCNXP_HAVE_MR0))
-- 
2.13.0