diff options
Diffstat (limited to 'drivers/i2c/bfin-twi_i2c.c')
| -rw-r--r-- | drivers/i2c/bfin-twi_i2c.c | 59 |
1 files changed, 48 insertions, 11 deletions
diff --git a/drivers/i2c/bfin-twi_i2c.c b/drivers/i2c/bfin-twi_i2c.c index 5ef30be..73a78d2 100644 --- a/drivers/i2c/bfin-twi_i2c.c +++ b/drivers/i2c/bfin-twi_i2c.c @@ -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) - ); - - /* Don't turn it on */ - bfin_write_TWI_MASTER_CTL(speed > 100000 ? FAST : 0); + i2c_set_bus_speed(speed); - /* But enable it */ + /* Enable it */ bfin_write_TWI_CONTROL(TWI_ENA | prescale); SSYNC(); |