[PATCH V2 5/6] regulator: add mxs on-chip regulator driver

[Stefan Wahren]

> Mark Brown <broonie at kernel.org> hat am 27. Mai 2015 um 19:33 geschrieben:
>
>
> On Tue, May 26, 2015 at 02:16:55PM +0200, Stefan Wahren wrote:
> > > Mark Brown <broonie at kernel.org> hat am 7. Mai 2015 um 21:32 geschrieben:
>
> > > > > > In the bootloader code enabling the DC-DC is critical. There is a
> > > > > > known
> > > > > > issue
> > > > > > which falsely triggers the brownout detection.
>
> > > > > Why would the driver not provide these operations?
>
> > > > I didn't implement this operation because the suggested workaround for
> > > > the
> > > > hardware issue isn't very nice
> > > > (disable brownout detection during enabling DC-DC). I was afraid of the
> > > > implementation.
>
> > > That doesn't sound too complicated?
>
> > Okay, i think i managed the brownout handling.
> >
> > Unfortunately i'm stuck at the next step. The DC-DC (3 way output) can
> > supply 3
> > LDOs vddd, vdda, vddio. In case of a DC-DC state change the 3 regulators
> > needs
> > to be reconfigured before.
>
> > I tought of REGULATOR_EVENT_PRE_DISABLE and REGULATOR_EVENT_PRE_ENABLE
> > events,
> > but i'm not sure that's the right way to achieve a synchronization between
> > DC-DC
> > and consuming LDOs.
>
> OK, that's possibly sounding a bit complicated. Is it just a case of
> writing some value, doing a reconfiguration and rewriting the original
> value or is it something more?

In case of a single driver instance instead of 4 ones (vddd, vddio, vdda,
dc-dc), things would be much easier.

Here are the steps for disabling DC-DC:

1. configure vddio to work without DC-DC
2. configure vdda to work without DC-DC
3. configure vddd to work without DC-DC
4. backup DC-DC settings
5. disable brownout detection
6. disable DC-DC
7. restore DC-DC settings

My problem is that step 1 to 3 must be done step by step through the other
regulator instances.

> If it's much more complicated than that
> then I think putting a comment in the driver explaining what the issue
> is would be the right step, that would address the issue with the driver
> looking strange.

Enabling or disabling DC-DC is only needed internally by the power subsystem
(e.g. in case of handoff AC to battery), because the DC-DC only supplys the
regulator daisy. From my understanding hardware components could use only the
regulator outputs. In the end a state change is necessary, but it shouldn't be a
public.