diff options
| -rw-r--r-- | drivers/marvell/i2c/a8k_i2c.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/drivers/marvell/i2c/a8k_i2c.c b/drivers/marvell/i2c/a8k_i2c.c index 1356fc07..c4ef1441 100644 --- a/drivers/marvell/i2c/a8k_i2c.c +++ b/drivers/marvell/i2c/a8k_i2c.c @@ -248,6 +248,20 @@ static int marvell_i2c_address_set(uint8_t chain, int command) return 0; } +/* + * The I2C module contains a clock divider to generate the SCL clock. + * This function calculates and sets the <N> and <M> fields in the I2C Baud + * Rate Register (t=01) to obtain given 'requested_speed'. + * The requested_speed will be equal to: + * CONFIG_SYS_TCLK / (10 * (M + 1) * (2 << N)) + * Where M is the value represented by bits[6:3] and N is the value represented + * by bits[2:0] of "I2C Baud Rate Register". + * Therefore max M which can be set is 16 (2^4) and max N is 8 (2^3). So the + * lowest possible baudrate is: + * CONFIG_SYS_TCLK/(10 * (16 +1) * (2 << 8), which equals to: + * CONFIG_SYS_TCLK/87040. Assuming that CONFIG_SYS_TCLK=250MHz, the lowest + * possible frequency is ~2,872KHz. + */ static unsigned int marvell_i2c_bus_speed_set(unsigned int requested_speed) { unsigned int n, m, freq, margin, min_margin = 0xffffffff; |