diff mbox

tty/serial: atmel: add fractional baud rate support

Message ID 20160825134756.6261-1-ludovic.desroches@atmel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Ludovic Desroches Aug. 25, 2016, 1:47 p.m. UTC 
The USART device provides a fractional baud rate generator to get a more
accurate baud rate. It can be used only when the USART is configured in
'normal mode' and this feature is not available on AT91RM9200 SoC.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
---
 drivers/tty/serial/atmel_serial.c | 41 +++++++++++++++++++++++++++++++--------
 include/linux/atmel_serial.h      |  1 +
 2 files changed, 34 insertions(+), 8 deletions(-)

Comments

Nicolas Ferre Aug. 25, 2016, 3:11 p.m. UTC | #1 
Le 25/08/2016 à 15:47, Ludovic Desroches a écrit :
> The USART device provides a fractional baud rate generator to get a more
> accurate baud rate. It can be used only when the USART is configured in
> 'normal mode' and this feature is not available on AT91RM9200 SoC.
> 
> Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>

Thanks, bye,

> ---
>  drivers/tty/serial/atmel_serial.c | 41 +++++++++++++++++++++++++++++++--------
>  include/linux/atmel_serial.h      |  1 +
>  2 files changed, 34 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index 2eaa18d..1759239 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -166,6 +166,7 @@ struct atmel_uart_port {
>  	u32			rts_low;
>  	bool			ms_irq_enabled;
>  	u32			rtor;	/* address of receiver timeout register if it exists */
> +	bool			has_frac_baudrate;
>  	bool			has_hw_timer;
>  	struct timer_list	uart_timer;
>  
> @@ -1745,6 +1746,11 @@ static void atmel_get_ip_name(struct uart_port *port)
>  	dbgu_uart = 0x44424755;	/* DBGU */
>  	new_uart = 0x55415254;	/* UART */
>  
> +	/*
> +	 * Only USART devices from at91sam9260 SOC implement fractional
> +	 * baudrate.
> +	 */
> +	atmel_port->has_frac_baudrate = false;
>  	atmel_port->has_hw_timer = false;
>  
>  	if (name == new_uart) {
> @@ -1753,6 +1759,7 @@ static void atmel_get_ip_name(struct uart_port *port)
>  		atmel_port->rtor = ATMEL_UA_RTOR;
>  	} else if (name == usart) {
>  		dev_dbg(port->dev, "Usart\n");
> +		atmel_port->has_frac_baudrate = true;
>  		atmel_port->has_hw_timer = true;
>  		atmel_port->rtor = ATMEL_US_RTOR;
>  	} else if (name == dbgu_uart) {
> @@ -1764,6 +1771,7 @@ static void atmel_get_ip_name(struct uart_port *port)
>  		case 0x302:
>  		case 0x10213:
>  			dev_dbg(port->dev, "This version is usart\n");
> +			atmel_port->has_frac_baudrate = true;
>  			atmel_port->has_hw_timer = true;
>  			atmel_port->rtor = ATMEL_US_RTOR;
>  			break;
> @@ -2025,8 +2033,9 @@ static void atmel_serial_pm(struct uart_port *port, unsigned int state,
>  static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>  			      struct ktermios *old)
>  {
> +	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
>  	unsigned long flags;
> -	unsigned int old_mode, mode, imr, quot, baud;
> +	unsigned int old_mode, mode, imr, quot, baud, div, cd, fp = 0;
>  
>  	/* save the current mode register */
>  	mode = old_mode = atmel_uart_readl(port, ATMEL_US_MR);
> @@ -2036,12 +2045,6 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>  		  ATMEL_US_PAR | ATMEL_US_USMODE);
>  
>  	baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk / 16);
> -	quot = uart_get_divisor(port, baud);
> -
> -	if (quot > 65535) {	/* BRGR is 16-bit, so switch to slower clock */
> -		quot /= 8;
> -		mode |= ATMEL_US_USCLKS_MCK_DIV8;
> -	}
>  
>  	/* byte size */
>  	switch (termios->c_cflag & CSIZE) {
> @@ -2160,7 +2163,29 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>  		atmel_uart_writel(port, ATMEL_US_CR, rts_state);
>  	}
>  
> -	/* set the baud rate */
> +	/*
> +	 * Set the baud rate:
> +	 * Fractional baudrate allows to setup output frequency more
> +	 * accurately. This feature is enabled only when using normal mode.
> +	 * baudrate = selected clock / (8 * (2 - OVER) * (CD + FP / 8))
> +	 * Currently, OVER is always set to 0 so we get
> +	 * baudrate = selected clock (16 * (CD + FP / 8))
> +	 */
> +	if (atmel_port->has_frac_baudrate &&
> +	    (mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_NORMAL) {
> +		div = DIV_ROUND_CLOSEST(port->uartclk, baud);
> +		cd = div / 16;
> +		fp = DIV_ROUND_CLOSEST(div % 16, 2);
> +	} else {
> +		cd = uart_get_divisor(port, baud);
> +	}
> +
> +	if (cd > 65535) {	/* BRGR is 16-bit, so switch to slower clock */
> +		cd /= 8;
> +		mode |= ATMEL_US_USCLKS_MCK_DIV8;
> +	}
> +	quot = cd | fp << ATMEL_US_FP_OFFSET;
> +
>  	atmel_uart_writel(port, ATMEL_US_BRGR, quot);
>  	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
>  	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);
> diff --git a/include/linux/atmel_serial.h b/include/linux/atmel_serial.h
> index 5a4d664..f8e452a 100644
> --- a/include/linux/atmel_serial.h
> +++ b/include/linux/atmel_serial.h
> @@ -118,6 +118,7 @@
>  
>  #define ATMEL_US_BRGR		0x20	/* Baud Rate Generator Register */
>  #define	ATMEL_US_CD		GENMASK(15, 0)	/* Clock Divider */
> +#define ATMEL_US_FP_OFFSET	16	/* Fractional Part */
>  
>  #define ATMEL_US_RTOR		0x24	/* Receiver Time-out Register for USART */
>  #define ATMEL_UA_RTOR		0x28	/* Receiver Time-out Register for UART */
>
diff mbox

Patch

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 2eaa18d..1759239 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -166,6 +166,7 @@  struct atmel_uart_port {
 	u32			rts_low;
 	bool			ms_irq_enabled;
 	u32			rtor;	/* address of receiver timeout register if it exists */
+	bool			has_frac_baudrate;
 	bool			has_hw_timer;
 	struct timer_list	uart_timer;
 
@@ -1745,6 +1746,11 @@  static void atmel_get_ip_name(struct uart_port *port)
 	dbgu_uart = 0x44424755;	/* DBGU */
 	new_uart = 0x55415254;	/* UART */
 
+	/*
+	 * Only USART devices from at91sam9260 SOC implement fractional
+	 * baudrate.
+	 */
+	atmel_port->has_frac_baudrate = false;
 	atmel_port->has_hw_timer = false;
 
 	if (name == new_uart) {
@@ -1753,6 +1759,7 @@  static void atmel_get_ip_name(struct uart_port *port)
 		atmel_port->rtor = ATMEL_UA_RTOR;
 	} else if (name == usart) {
 		dev_dbg(port->dev, "Usart\n");
+		atmel_port->has_frac_baudrate = true;
 		atmel_port->has_hw_timer = true;
 		atmel_port->rtor = ATMEL_US_RTOR;
 	} else if (name == dbgu_uart) {
@@ -1764,6 +1771,7 @@  static void atmel_get_ip_name(struct uart_port *port)
 		case 0x302:
 		case 0x10213:
 			dev_dbg(port->dev, "This version is usart\n");
+			atmel_port->has_frac_baudrate = true;
 			atmel_port->has_hw_timer = true;
 			atmel_port->rtor = ATMEL_US_RTOR;
 			break;
@@ -2025,8 +2033,9 @@  static void atmel_serial_pm(struct uart_port *port, unsigned int state,
 static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
 			      struct ktermios *old)
 {
+	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
 	unsigned long flags;
-	unsigned int old_mode, mode, imr, quot, baud;
+	unsigned int old_mode, mode, imr, quot, baud, div, cd, fp = 0;
 
 	/* save the current mode register */
 	mode = old_mode = atmel_uart_readl(port, ATMEL_US_MR);
@@ -2036,12 +2045,6 @@  static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
 		  ATMEL_US_PAR | ATMEL_US_USMODE);
 
 	baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk / 16);
-	quot = uart_get_divisor(port, baud);
-
-	if (quot > 65535) {	/* BRGR is 16-bit, so switch to slower clock */
-		quot /= 8;
-		mode |= ATMEL_US_USCLKS_MCK_DIV8;
-	}
 
 	/* byte size */
 	switch (termios->c_cflag & CSIZE) {
@@ -2160,7 +2163,29 @@  static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
 		atmel_uart_writel(port, ATMEL_US_CR, rts_state);
 	}
 
-	/* set the baud rate */
+	/*
+	 * Set the baud rate:
+	 * Fractional baudrate allows to setup output frequency more
+	 * accurately. This feature is enabled only when using normal mode.
+	 * baudrate = selected clock / (8 * (2 - OVER) * (CD + FP / 8))
+	 * Currently, OVER is always set to 0 so we get
+	 * baudrate = selected clock (16 * (CD + FP / 8))
+	 */
+	if (atmel_port->has_frac_baudrate &&
+	    (mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_NORMAL) {
+		div = DIV_ROUND_CLOSEST(port->uartclk, baud);
+		cd = div / 16;
+		fp = DIV_ROUND_CLOSEST(div % 16, 2);
+	} else {
+		cd = uart_get_divisor(port, baud);
+	}
+
+	if (cd > 65535) {	/* BRGR is 16-bit, so switch to slower clock */
+		cd /= 8;
+		mode |= ATMEL_US_USCLKS_MCK_DIV8;
+	}
+	quot = cd | fp << ATMEL_US_FP_OFFSET;
+
 	atmel_uart_writel(port, ATMEL_US_BRGR, quot);
 	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
 	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);
diff --git a/include/linux/atmel_serial.h b/include/linux/atmel_serial.h
index 5a4d664..f8e452a 100644
--- a/include/linux/atmel_serial.h
+++ b/include/linux/atmel_serial.h
@@ -118,6 +118,7 @@ 
 
 #define ATMEL_US_BRGR		0x20	/* Baud Rate Generator Register */
 #define	ATMEL_US_CD		GENMASK(15, 0)	/* Clock Divider */
+#define ATMEL_US_FP_OFFSET	16	/* Fractional Part */
 
 #define ATMEL_US_RTOR		0x24	/* Receiver Time-out Register for USART */
 #define ATMEL_UA_RTOR		0x28	/* Receiver Time-out Register for UART */