From 2dff8ad92661b6c99e9ba8b5918e43b522551556 Mon Sep 17 00:00:00 2001 From: Gabor Juhos Date: Wed, 14 Nov 2012 10:38:13 +0100 Subject: [PATCH] tty/serial/ar933x_uart: fix baud rate calculation commit 2dff8ad92661b6c99e9ba8b5918e43b522551556 upstream. The UART of the AR933x SoC implements a fractional divisor for generating the desired baud rate. The current code uses a fixed value for the fractional part of the divisor, and this leads to improperly calculated baud rates: baud scale step real baud diff 300 5207* 8192 17756 17456 5818.66% 600 2603* 8192 35511 34911 5818.50% 1200 1301* 8192 71023 69823 5818.58% 2400 650* 8192 11241 8841 368.37% 4800 324* 8192 22645 17845 371.77% 9600 161 8192 9645 45 0.46% 14400 107 8192 14468 68 0.47% 19200 80 8192 19290 90 0.46% 28800 53 8192 28935 135 0.46% 38400 39 8192 39063 663 1.72% 57600 26 8192 57870 270 0.46% 115200 12 8192 120192 4992 4.33% 230400 5 8192 260417 30017 13.02% 460800 2 8192 520833 60033 13.02% 921600 0 8192 1562500 640900 69.93% After the patch, the integer and fractional parts of the divisor will be calculated dynamically. This ensures that the UART will use correct baud rates: baud scale step real baud diff 300 6 11 300 0 0.00% 600 54 173 600 0 0.00% 1200 30 195 1200 0 0.00% 2400 30 390 2400 0 0.00% 4800 48 1233 4800 0 0.00% 9600 78 3976 9600 0 0.00% 14400 98 7474 14400 0 0.00% 19200 55 5637 19200 0 0.00% 28800 130 19780 28800 0 0.00% 38400 36 7449 38400 0 0.00% 57600 78 23857 57600 0 0.00% 115200 43 26575 115200 0 0.00% 230400 23 28991 230400 0 0.00% 460800 11 28991 460800 0 0.00% 921600 5 28991 921599 -1 0.00% Signed-off-by: Gabor Juhos Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/ar933x_uart.c | 90 +++++++++++++++++++++++++++++++++++--- 1 file changed, 85 insertions(+), 5 deletions(-) --- a/drivers/tty/serial/ar933x_uart.c +++ b/drivers/tty/serial/ar933x_uart.c @@ -25,11 +25,19 @@ #include #include +#include + #include #include #define DRIVER_NAME "ar933x-uart" +#define AR933X_UART_MAX_SCALE 0xff +#define AR933X_UART_MAX_STEP 0xffff + +#define AR933X_UART_MIN_BAUD 300 +#define AR933X_UART_MAX_BAUD 3000000 + #define AR933X_DUMMY_STATUS_RD 0x01 static struct uart_driver ar933x_uart_driver; @@ -37,6 +45,8 @@ static struct uart_driver ar933x_uart_dr struct ar933x_uart_port { struct uart_port port; unsigned int ier; /* shadow Interrupt Enable Register */ + unsigned int min_baud; + unsigned int max_baud; }; static inline unsigned int ar933x_uart_read(struct ar933x_uart_port *up, @@ -162,6 +172,57 @@ static void ar933x_uart_enable_ms(struct { } +/* + * baudrate = (clk / (scale + 1)) * (step * (1 / 2^17)) + */ +static unsigned long ar933x_uart_get_baud(unsigned int clk, + unsigned int scale, + unsigned int step) +{ + u64 t; + u32 div; + + div = (2 << 16) * (scale + 1); + t = clk; + t *= step; + t += (div / 2); + do_div(t, div); + + return t; +} + +static void ar933x_uart_get_scale_step(unsigned int clk, + unsigned int baud, + unsigned int *scale, + unsigned int *step) +{ + unsigned int tscale; + long min_diff; + + *scale = 0; + *step = 0; + + min_diff = baud; + for (tscale = 0; tscale < AR933X_UART_MAX_SCALE; tscale++) { + u64 tstep; + int diff; + + tstep = baud * (tscale + 1); + tstep *= (2 << 16); + do_div(tstep, clk); + + if (tstep > AR933X_UART_MAX_STEP) + break; + + diff = abs(ar933x_uart_get_baud(clk, tscale, tstep) - baud); + if (diff < min_diff) { + min_diff = diff; + *scale = tscale; + *step = tstep; + } + } +} + static void ar933x_uart_set_termios(struct uart_port *port, struct ktermios *new, struct ktermios *old) @@ -169,7 +230,7 @@ static void ar933x_uart_set_termios(stru struct ar933x_uart_port *up = (struct ar933x_uart_port *) port; unsigned int cs; unsigned long flags; - unsigned int baud, scale; + unsigned int baud, scale, step; /* Only CS8 is supported */ new->c_cflag &= ~CSIZE; @@ -191,8 +252,8 @@ static void ar933x_uart_set_termios(stru /* Mark/space parity is not supported */ new->c_cflag &= ~CMSPAR; - baud = uart_get_baud_rate(port, new, old, 0, port->uartclk / 16); - scale = (port->uartclk / (16 * baud)) - 1; + baud = uart_get_baud_rate(port, new, old, up->min_baud, up->max_baud); + ar933x_uart_get_scale_step(port->uartclk, baud, &scale, &step); /* * Ok, we're now changing the port state. Do it with @@ -200,6 +261,10 @@ static void ar933x_uart_set_termios(stru */ spin_lock_irqsave(&up->port.lock, flags); + /* disable the UART */ + ar933x_uart_rmw_clear(up, AR933X_UART_CS_REG, + AR933X_UART_CS_IF_MODE_M << AR933X_UART_CS_IF_MODE_S); + /* Update the per-port timeout. */ uart_update_timeout(port, new->c_cflag, baud); @@ -210,7 +275,7 @@ static void ar933x_uart_set_termios(stru up->port.ignore_status_mask |= AR933X_DUMMY_STATUS_RD; ar933x_uart_write(up, AR933X_UART_CLOCK_REG, - scale << AR933X_UART_CLOCK_SCALE_S | 8192); + scale << AR933X_UART_CLOCK_SCALE_S | step); /* setup configuration register */ ar933x_uart_rmw(up, AR933X_UART_CS_REG, AR933X_UART_CS_PARITY_M, cs); @@ -219,6 +284,11 @@ static void ar933x_uart_set_termios(stru ar933x_uart_rmw_set(up, AR933X_UART_CS_REG, AR933X_UART_CS_HOST_INT_EN); + /* reenable the UART */ + ar933x_uart_rmw(up, AR933X_UART_CS_REG, + AR933X_UART_CS_IF_MODE_M << AR933X_UART_CS_IF_MODE_S, + AR933X_UART_CS_IF_MODE_DCE << AR933X_UART_CS_IF_MODE_S); + spin_unlock_irqrestore(&up->port.lock, flags); if (tty_termios_baud_rate(new)) @@ -401,6 +471,8 @@ static void ar933x_uart_config_port(stru static int ar933x_uart_verify_port(struct uart_port *port, struct serial_struct *ser) { + struct ar933x_uart_port *up = (struct ar933x_uart_port *) port; + if (ser->type != PORT_UNKNOWN && ser->type != PORT_AR933X) return -EINVAL; @@ -408,7 +480,8 @@ static int ar933x_uart_verify_port(struc if (ser->irq < 0 || ser->irq >= NR_IRQS) return -EINVAL; - if (ser->baud_base < 28800) + if (ser->baud_base < up->min_baud || + ser->baud_base > up->max_baud) return -EINVAL; return 0; @@ -561,6 +634,7 @@ static int __devinit ar933x_uart_probe(s struct uart_port *port; struct resource *mem_res; struct resource *irq_res; + unsigned int baud; int id; int ret; @@ -611,6 +685,12 @@ static int __devinit ar933x_uart_probe(s port->fifosize = AR933X_UART_FIFO_SIZE; port->ops = &ar933x_uart_ops; + baud = ar933x_uart_get_baud(port->uartclk, AR933X_UART_MAX_SCALE, 1); + up->min_baud = max_t(unsigned int, baud, AR933X_UART_MIN_BAUD); + + baud = ar933x_uart_get_baud(port->uartclk, 0, AR933X_UART_MAX_STEP); + up->max_baud = min_t(unsigned int, baud, AR933X_UART_MAX_BAUD); + ar933x_uart_add_console_port(up); ret = uart_add_one_port(&ar933x_uart_driver, &up->port);