tty/serial/ar933x_uart: fix baud rate calculation

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 <juhosg@openwrt.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Gabor Juhos 2012-11-14 10:38:13 +01:00 committed by Greg Kroah-Hartman
parent 5318609519
commit 2dff8ad926

View file

@ -25,11 +25,19 @@
#include <linux/io.h>
#include <linux/irq.h>
#include <asm/div64.h>
#include <asm/mach-ath79/ar933x_uart.h>
#include <asm/mach-ath79/ar933x_uart_platform.h>
#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_driver;
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 uart_port *port)
{
}
/*
* 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(struct uart_port *port,
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(struct uart_port *port,
/* 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(struct uart_port *port,
*/
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(struct uart_port *port,
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(struct uart_port *port,
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(struct uart_port *port, int flags)
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(struct uart_port *port,
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(struct platform_device *pdev)
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(struct platform_device *pdev)
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);