Re: [PATCH 1/2] regulator: DT: Add support to scale ramp delay based on platform behavior

[Laxman Dewangan]

On Tuesday 01 March 2016 07:53 AM, Mark Brown wrote:
> * PGP Signed by an unknown key
>
> On Mon, Feb 29, 2016 at 09:47:51AM -0800, Bjorn Andersson wrote:
> > On Mon 29 Feb 06:40 PST 2016, Laxman Dewangan wrote:
> > > It is observed that voltage change in given rail affected by the load
> > > and the capacitor in the rail. This may cause the slow ramp in voltage
> > > against what PMIC has programmed.
> > The regulator-ramp-delay is a variable you can tweak on a board basis,
> > so I'm not sure what benefit it gives to be able to add a scaling
> > factor to this.
> > In my experience your HW engineer will say "you have to wait X ms", not
> > "you have to wait 125% of X ms".
> > Can you please elaborate on why the original knob isn't sufficient?
> Right, this definitely feels like the wrong thing is being specified
> here (and also like the PMIC might be going out of spec, possibly as a
> result of being overloaded) and that the existing board specific
> controls should be used.  It just doesn't correspond to the way people
> usually talk about specs for PMICs.

Most of PMICs offer to configure the slew rate (ramp time). For 
discussion, I am considering MAX77620 LDOs provides option to 27mV/us 
and 100mV/us.

HW team characterize the board and its rail and come up with the 
following data:
- Configure PMIC to 27mV/us for ramp time.
- With this measured value of ramp on board is 10mV/us and it is safe 
to  assume 5mv/us to consider the board variations.

So we have now two input from HW team:
1. What should be configure in PMIC.
2. And for calculation, how much ramp need to be consider.

For (1), it is 25mV/us and for (2) which 540% (27 *100/5).

Currently, we can provide the 27mv/us as ramp-delay but do not have 
option for scaling it.

My patch add for knob for (2).