In Designware I2C Uboot driver, the HCNT calculation in Fast plus mode(1MHZ clock transfer rate) seems to be incorrect with default values present in the driver.
In function, dw_i2c_calc_timing(), hcnt is being calculated using below formula:-
"hcnt = min_thigh_cnt - fall_cnt - 7 - spk_cnt;"
With 1MHz tranfer rate and default values from the driver, min_thigh_cnt is computed to be 26, fall_cnt to 50, and spk_cnt is 0.
So, hcnt comes out to be:- 26 - 50 - 7 - 0 = -31.
And as Hcnt comes out to be negative, the further check fails which checks if either of hcnt or lcnt is negative, then return unsuccessful status:-
if (hcnt < 0 || lcnt < 0) { debug("dw_i2c: bad counts. hcnt = %d lcnt = %d\n", hcnt, lcnt); return log_msg_ret("counts", -EINVAL); }
This appears to be failing for the higher transfer rates as well, i.e. High speed mode as well.
Can someone confirm if this logic is correct?
Regards Manav