[PATCH] ARM: PL011 baudrate extension for ST-Ericssons derivative

[Linus Walleij]

Implementation of the ST-Ericsson baudrate extension in the PL011
block. In this modified variant it is possible to change the
sampling factor from 16 to 8, and thanks to this we can get higher
baudrates while still using the same peripheral clock.

Also replace the simple division to determine the baud divisor
with DIV_ROUND_CLOSEST() rather than a simple integer division.

Cc: Alessandro Rubini <rubini at unipv.it>
Cc: Jerzy Kasenberg <jerzy.kasenberg at tieto.com>
Signed-off-by: Marcin Mielczarczyk <marcin.mielczarczyk at tieto.com>
Signed-off-by: Linus Walleij <linus.walleij at stericsson.com>
---
Resending this not purely for the joy of seeing our whitespace
fixes, but for the fact that we also introduced DIV_ROUND_CLOSEST()
to calculate the divisor value.
---
 drivers/serial/amba-pl011.c |   27 +++++++++++++++++++++++++--
 include/linux/amba/serial.h |    1 +
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/drivers/serial/amba-pl011.c b/drivers/serial/amba-pl011.c
index 5644cf2..f67e09d 100644
--- a/drivers/serial/amba-pl011.c
+++ b/drivers/serial/amba-pl011.c
@@ -74,6 +74,7 @@ struct uart_amba_port {
 	unsigned int		ifls;		/* vendor-specific */
 	unsigned int		lcrh_tx;	/* vendor-specific */
 	unsigned int		lcrh_rx;	/* vendor-specific */
+	bool			oversampling;   /* vendor-specific */
 	bool			autorts;
 };
 
@@ -83,6 +84,7 @@ struct vendor_data {
 	unsigned int		fifosize;
 	unsigned int		lcrh_tx;
 	unsigned int		lcrh_rx;
+	bool			oversampling;
 };
 
 static struct vendor_data vendor_arm = {
@@ -90,6 +92,7 @@ static struct vendor_data vendor_arm = {
 	.fifosize		= 16,
 	.lcrh_tx		= UART011_LCRH,
 	.lcrh_rx		= UART011_LCRH,
+	.oversampling		= false,
 };
 
 static struct vendor_data vendor_st = {
@@ -97,6 +100,7 @@ static struct vendor_data vendor_st = {
 	.fifosize		= 64,
 	.lcrh_tx		= ST_UART011_LCRH_TX,
 	.lcrh_rx		= ST_UART011_LCRH_RX,
+	.oversampling		= true,
 };
 
 static void pl011_stop_tx(struct uart_port *port)
@@ -499,8 +503,13 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
 	/*
 	 * Ask the core to calculate the divisor for us.
 	 */
-	baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
-	quot = port->uartclk * 4 / baud;
+	baud = uart_get_baud_rate(port, termios, old, 0,
+				  port->uartclk/(uap->oversampling ? 8 : 16));
+
+	if (baud > port->uartclk/16)
+		quot = DIV_ROUND_CLOSEST(port->uartclk * 8, baud);
+	else
+		quot = DIV_ROUND_CLOSEST(port->uartclk * 4, baud);
 
 	switch (termios->c_cflag & CSIZE) {
 	case CS5:
@@ -579,6 +588,13 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
 		uap->autorts = false;
 	}
 
+	if (uap->oversampling) {
+		if (baud > port->uartclk/16)
+			old_cr |= ST_UART011_CR_OVSFACT;
+		else
+			old_cr &= ~ST_UART011_CR_OVSFACT;
+	}
+
 	/* Set baud rate */
 	writew(quot & 0x3f, port->membase + UART011_FBRD);
 	writew(quot >> 6, port->membase + UART011_IBRD);
@@ -744,6 +760,12 @@ pl011_console_get_options(struct uart_amba_port *uap, int *baud,
 		fbrd = readw(uap->port.membase + UART011_FBRD);
 
 		*baud = uap->port.uartclk * 4 / (64 * ibrd + fbrd);
+
+		if (uap->oversampling) {
+			if (readw(uap->port.membase + UART011_CR)
+				  & ST_UART011_CR_OVSFACT)
+				*baud *= 2;
+		}
 	}
 }
 
@@ -839,6 +861,7 @@ static int pl011_probe(struct amba_device *dev, struct amba_id *id)
 	uap->ifls = vendor->ifls;
 	uap->lcrh_rx = vendor->lcrh_rx;
 	uap->lcrh_tx = vendor->lcrh_tx;
+	uap->oversampling = vendor->oversampling;
 	uap->port.dev = &dev->dev;
 	uap->port.mapbase = dev->res.start;
 	uap->port.membase = base;
diff --git a/include/linux/amba/serial.h b/include/linux/amba/serial.h
index 93c96a6..e1b634b 100644
--- a/include/linux/amba/serial.h
+++ b/include/linux/amba/serial.h
@@ -86,6 +86,7 @@
 #define UART010_CR_TIE 		0x0020
 #define UART010_CR_RIE 		0x0010
 #define UART010_CR_MSIE		0x0008
+#define ST_UART011_CR_OVSFACT	0x0008	/* Oversampling factor */
 #define UART01x_CR_IIRLP	0x0004	/* SIR low power mode */
 #define UART01x_CR_SIREN	0x0002	/* SIR enable */
 #define UART01x_CR_UARTEN	0x0001	/* UART enable */
-- 
1.6.3.3