[PATCH 11/11] serial: sh-sci: Rework baud rate calculation

[Simon Horman]

From: Laurent Pinchart <laurent.pinchart+renesas at ideasonboard.com>

Computing the baud rate register value requires knowledge of the
hardware sampling rate. This information is currently encoded in a baud
rate calculation algorithm ID passed through platform data. However, it
can be derived from the port type directly in most cases.

Compute the sampling rate internally in the driver if the baud rate
calculation algorithm ID isn't specified, and allow platforms to
override the sampling rate through platform data in special cases (this
is only required for SCIFA ports on sh7723 and sh7724, the reason needs
to be investigated).

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas at ideasonboard.com>
Acked-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Simon Horman <horms+renesas at verge.net.au>
---
 drivers/tty/serial/sh-sci.c | 37 ++++++++++++++++++++++++++++++-------
 include/linux/serial_sci.h  |  2 ++
 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index d5239d5..e4bf0e4 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -65,6 +65,7 @@ struct sci_port {
 	struct plat_sci_port	*cfg;
 	int			overrun_bit;
 	unsigned int		error_mask;
+	unsigned int		sampling_rate;
 
 
 	/* Break timer */
@@ -1750,10 +1751,13 @@ static void sci_shutdown(struct uart_port *port)
 	sci_free_irq(s);
 }
 
-static unsigned int sci_scbrr_calc(unsigned int algo_id, unsigned int bps,
+static unsigned int sci_scbrr_calc(struct sci_port *s, unsigned int bps,
 				   unsigned long freq)
 {
-	switch (algo_id) {
+	if (s->sampling_rate)
+		return DIV_ROUND_CLOSEST(freq, s->sampling_rate * bps) - 1;
+
+	switch (s->cfg->scbrr_algo_id) {
 	case SCBRR_ALGO_1:
 		return freq / (16 * bps);
 	case SCBRR_ALGO_2:
@@ -1843,12 +1847,11 @@ 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->scbrr_algo_id == SCBRR_ALGO_6) {
+		if (s->cfg->type == PORT_HSCIF) {
 			sci_baud_calc_hscif(baud, port->uartclk, &t, &srr,
 					    &cks);
 		} else {
-			t = sci_scbrr_calc(s->cfg->scbrr_algo_id, baud,
-					   port->uartclk);
+			t = sci_scbrr_calc(s, baud, port->uartclk);
 			for (cks = 0; t >= 256 && cks <= 3; cks++)
 				t >>= 2;
 		}
@@ -2092,6 +2095,7 @@ static int sci_init_single(struct platform_device *dev,
 {
 	struct uart_port *port = &sci_port->port;
 	const struct resource *res;
+	unsigned int sampling_rate;
 	unsigned int i;
 	int ret;
 
@@ -2143,28 +2147,47 @@ static int sci_init_single(struct platform_device *dev,
 	case PORT_SCIFB:
 		port->fifosize = 256;
 		sci_port->overrun_bit = 9;
+		sampling_rate = 16;
 		break;
 	case PORT_HSCIF:
 		port->fifosize = 128;
+		sampling_rate = 0;
 		sci_port->overrun_bit = 0;
 		break;
 	case PORT_SCIFA:
 		port->fifosize = 64;
 		sci_port->overrun_bit = 9;
+		sampling_rate = 16;
 		break;
 	case PORT_SCIF:
 		port->fifosize = 16;
-		if (p->regtype == SCIx_SH7705_SCIF_REGTYPE)
+		if (p->regtype == SCIx_SH7705_SCIF_REGTYPE) {
 			sci_port->overrun_bit = 9;
-		else
+			sampling_rate = 16;
+		} else {
 			sci_port->overrun_bit = 0;
+			sampling_rate = 32;
+		}
 		break;
 	default:
 		port->fifosize = 1;
 		sci_port->overrun_bit = 5;
+		sampling_rate = 32;
 		break;
 	}
 
+	/* Set the sampling rate if the baud rate calculation algorithm isn't
+	 * specified.
+	 */
+	if (p->scbrr_algo_id == SCBRR_ALGO_NONE) {
+		/* SCIFA on sh7723 and sh7724 need a custom sampling rate that
+		 * doesn't match the SoC datasheet, this should be investigated.
+		 * Let platform data override the sampling rate for now.
+		 */
+		sci_port->sampling_rate = p->sampling_rate ? p->sampling_rate
+					: sampling_rate;
+	}
+
 	if (!early) {
 		sci_port->iclk = clk_get(&dev->dev, "sci_ick");
 		if (IS_ERR(sci_port->iclk)) {
diff --git a/include/linux/serial_sci.h b/include/linux/serial_sci.h
index e9c3021..af414e1 100644
--- a/include/linux/serial_sci.h
+++ b/include/linux/serial_sci.h
@@ -11,6 +11,7 @@
 #define SCIx_NOT_SUPPORTED	(-1)
 
 enum {
+	SCBRR_ALGO_NONE,	/* Compute sampling rate in the driver */
 	SCBRR_ALGO_1,		/* clk / (16 * bps) */
 	SCBRR_ALGO_2,		/* DIV_ROUND_CLOSEST(clk, 32 * bps) - 1 */
 	SCBRR_ALGO_3,		/* clk / (8 * bps) */
@@ -134,6 +135,7 @@ struct plat_sci_port {
 	upf_t		flags;			/* UPF_* flags */
 	unsigned long	capabilities;		/* Port features/capabilities */
 
+	unsigned int	sampling_rate;
 	unsigned int	scbrr_algo_id;		/* SCBRR calculation algo */
 	unsigned int	scscr;			/* SCSCR initialization */
 
-- 
1.8.4