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

From: Laxman Dewangan
Date: Mon Feb 29 2016 - 23:01:26 EST

On Tuesday 01 March 2016 07:53 AM, Mark Brown wrote:
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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).