[U-Boot] mxs: Possible in bug in mxs_enable_4p2_dcdc_input

Marek Vasut
2015-05-13T20:03:25Z

On Wednesday, May 13, 2015 at 10:14:19 AM, Stefan Wahren wrote:
> Hi Marek,
>
> Am 13.05.2015 um 09:13 schrieb Marek Vasut:
> > On Wednesday, May 13, 2015 at 08:02:21 AM, Stefan Wahren wrote:
> >> Hi,
> >
> > Hi,
> >
> >> during the study of DC-DC handling in u-boot i noticed a possible bug.
> >>
> >> In case the DC-DC is already enabled the function returns without
> >> reenabling brown out detection. I don't think that's okay.
> >> A possible fix would be to do the check if DC-DC is already enabled
> >> before disabling brown out detection. This idea is
> >> attached as a draft. If it's acceptable i will send a proper patch.
> >
> > What exactly would happen if you enable DCDC converter while BO detection
> > is already enabled ? It is possible, that enabling the DCDC would cause a
> > dip on the power rail and cause in turn a BO, no ? IIRC, that is the
> > reason why BO detection is disabled when enabling DCDC.
>
> i think we're talking about different things. The patch won't touch this
> necessary behaviour.
>
> No, i think it's faulty to leave the function with BO detection disabled
> in the case the DC-DC is already enabled:
>
> if (xfer && (readl(&power_regs->hw_power_5vctrl) &
> POWER_5VCTRL_ENABLE_DCDC)) {
> return;
> }

Uh uh, I'm an idiot and I was probably half asleep when I blurted this last
mail, sorry.

Obviously, enabling the BO properly makes sense.

Best regards,
Marek Vasut