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    SubjectRe: [PATCH 1/2] regulator: DT: Add support to scale ramp delay based on platform behavior
    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 property regulator-ramp-delay provides the ramp delay configuration
    > for PMIC but actual voltage settling time may change based on platform.
    >
    > Add new property "regulator-ramp-delay-scale" for platform specific scaling
    > in final ramp delay calculation. On this case, final wait delay time
    > for voltage change is calculated as the
    > DIV_ROUND_UP(ramp_delay * ramp_delay_scale, 100)
    >
    > The value is provided in the term of percentage i.e. 300% means it will
    > do the 3x delay of calculated value.
    >
    > Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
    > ---

    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?

    Regards,
    Bjorn

    > Documentation/devicetree/bindings/regulator/regulator.txt | 7 +++++++
    > 1 file changed, 7 insertions(+)
    >
    > diff --git a/Documentation/devicetree/bindings/regulator/regulator.txt b/Documentation/devicetree/bindings/regulator/regulator.txt
    > index 1d112fc..f2e8360 100644
    > --- a/Documentation/devicetree/bindings/regulator/regulator.txt
    > +++ b/Documentation/devicetree/bindings/regulator/regulator.txt
    > @@ -16,6 +16,13 @@ Optional properties:
    > - regulator-ramp-delay: ramp delay for regulator(in uV/uS)
    > For hardware which supports disabling ramp rate, it should be explicitly
    > initialised to zero (regulator-ramp-delay = <0>) for disabling ramp delay.
    > +- regulator-ramp-delay-scale: Platform specific scaling in ramp delay to
    > + provide extra guard time to settle down voltage after its change. This will
    > + help to wait for extra time for voltage settling based on platform behavior.
    > + This is provided in terms of percentage scaling like 300% means final delay
    > + will become 3x of calculated ramp delay for voltage change.
    > + The final delay is calculated as:
    > + delay = DIV_ROUND_UP(ramp-delay * ramp-delay-scale, 100)
    > - regulator-enable-ramp-delay: The time taken, in microseconds, for the supply
    > rail to reach the target voltage, plus/minus whatever tolerance the board
    > design requires. This property describes the total system ramp time
    > --
    > 2.1.4
    >

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