Designware i2c driver, HCNT calculation logic

[Manav Bedi]

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