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Blackfin: TWI/I2C: implement bus speed get/set functions 

While we're here, improve the speed calculation a bit to match the HRM.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
This commit is contained in:
Mike Frysinger 2009-10-14 19:27:27 -04:00 committed by Heiko Schocher
parent 3814ea4f00
commit 08a1c6258c
1 changed files with 48 additions and 11 deletions
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59
drivers/i2c/bfin-twi_i2c.c
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@ -26,6 +26,7 @@
#ifdef TWI0_CLKDIV
#define bfin_write_TWI_CLKDIV(val) bfin_write_TWI0_CLKDIV(val)
#define bfin_read_TWI_CLKDIV(val) bfin_read_TWI0_CLKDIV(val)
#define bfin_write_TWI_CONTROL(val) bfin_write_TWI0_CONTROL(val)
#define bfin_read_TWI_CONTROL(val) bfin_read_TWI0_CONTROL(val)
#define bfin_write_TWI_MASTER_ADDR(val) bfin_write_TWI0_MASTER_ADDR(val)
@ -44,8 +45,21 @@
#ifdef CONFIG_TWICLK_KHZ
# error do not define CONFIG_TWICLK_KHZ ... use CONFIG_SYS_I2C_SPEED
#endif
#if CONFIG_SYS_I2C_SPEED > 400000
# error The Blackfin I2C hardware can only operate at 400KHz max
/*
* The way speed is changed into duty often results in integer truncation
* with 50% duty, so we'll force rounding up to the next duty by adding 1
* to the max. In practice this will get us a speed of something like
* 385 KHz. The other limit is easy to handle as it is only 8 bits.
*/
#define I2C_SPEED_MAX 400000
#define I2C_SPEED_TO_DUTY(speed) (5000000 / (speed))
#define I2C_DUTY_MAX (I2C_SPEED_TO_DUTY(I2C_SPEED_MAX) + 1)
#define I2C_DUTY_MIN 0xff /* 8 bit limited */
#define SYS_I2C_DUTY I2C_SPEED_TO_DUTY(CONFIG_SYS_I2C_SPEED)
/* Note: duty is inverse of speed, so the comparisons below are correct */
#if SYS_I2C_DUTY < I2C_DUTY_MAX || SYS_I2C_DUTY > I2C_DUTY_MIN
# error "The Blackfin I2C hardware can only operate 20KHz - 400KHz"
#endif
/* All transfers are described by this data structure */
@ -213,7 +227,36 @@ static int i2c_transfer(uchar chip, uint addr, int alen, uchar *buffer, int len,
return ret;
}
/*
/**
* i2c_set_bus_speed - set i2c bus speed
* @speed: bus speed (in HZ)
*/
int i2c_set_bus_speed(unsigned int speed)
{
u16 clkdiv = I2C_SPEED_TO_DUTY(speed);
/* Set TWI interface clock */
if (clkdiv < I2C_DUTY_MAX || clkdiv > I2C_DUTY_MIN)
return -1;
bfin_write_TWI_CLKDIV((clkdiv << 8) | (clkdiv & 0xff));
/* Don't turn it on */
bfin_write_TWI_MASTER_CTL(speed > 100000 ? FAST : 0);
return 0;
}
/**
* i2c_get_bus_speed - get i2c bus speed
* @speed: bus speed (in HZ)
*/
unsigned int i2c_get_bus_speed(void)
{
/* 10 MHz / (2 * CLKDIV) -> 5 MHz / CLKDIV */
return 5000000 / (bfin_read_TWI_CLKDIV() & 0xff);
}
/**
* i2c_init - initialize the i2c bus
* @speed: bus speed (in HZ)
* @slaveaddr: address of device in slave mode (0 - not slave)
@ -229,15 +272,9 @@ void i2c_init(int speed, int slaveaddr)
bfin_write_TWI_CONTROL(prescale);
/* Set TWI interface clock as specified */
bfin_write_TWI_CLKDIV(
((5 * 1024 / (speed / 1000)) << 8) |
((5 * 1024 / (speed / 1000)) & 0xFF)
);
i2c_set_bus_speed(speed);
/* Don't turn it on */
bfin_write_TWI_MASTER_CTL(speed > 100000 ? FAST : 0);
/* But enable it */
/* Enable it */
bfin_write_TWI_CONTROL(TWI_ENA | prescale);
SSYNC();