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

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Date:	Mon, 29 Feb 2016 20:10:28 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	<broonie@...nel.org>, <robh+dt@...nel.org>, <pawel.moll@....com>,
	<mark.rutland@....com>, <ijc+devicetree@...lion.org.uk>
CC:	<lgirdwood@...il.com>, <bjorn.andersson@...ymobile.com>,
	<swarren@...dotorg.org>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Laxman Dewangan <ldewangan@...dia.com>
Subject: [PATCH 1/2] regulator: DT: Add support to scale ramp delay based on platform behavior

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@...dia.com>
---
 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