linux-kernel - Re: [PATCH V2] regulator: core: add support for configuring turn-on time through constraints

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Date:	Wed, 11 Sep 2013 23:16:06 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	"broonie@...nel.org" <broonie@...nel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"rob@...dley.net" <rob@...dley.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lgirdwood@...il.com" <lgirdwood@...il.com>
Subject: Re: [PATCH V2] regulator: core: add support for configuring turn-on
 time through constraints

On Wednesday 11 September 2013 10:47 PM, Stephen Warren wrote:
> On 09/11/2013 06:58 AM, Laxman Dewangan wrote:
>> The Turn-on time of the regulator depends on the regulator device's
>> electrical characteristics. Sometimes regulator turn-on time also
>> depends on the capacitive load on the given platform and it can be
>> more than the datasheet value.
>>
>> The driver provides the enable-time as per datasheet.
>>
>> Add support for configure the enable ramp time through regulator
>> constraints so that regulator core can take this value for enable
>> time for that regulator.
>> diff --git a/Documentation/devicetree/bindings/regulator/regulator.txt b/Documentation/devicetree/bindings/regulator/regulator.txt
>>   - regulator-ramp-delay: ramp delay for regulator(in uV/uS)
>>     For hardwares which support disabling ramp rate, it should be explicitly
>>     intialised to zero (regulator-ramp-delay = <0>) for disabling ramp delay.
>> +- regulator-enable-ramp-delay: Turn-on time for regulator(in uSec). This is
>> +  the time time taken to reach within some proportion of the target voltage
>> +  from off state.
> This is still a bit unclear. What proportion of the target voltage?
> There's no mention that this describes the delay due to the
> board/environment rather than the delay due to the internal operation of
> the regulator itself. How about:
>
> - regulator-enable-ramp-delay: The time taken, in uSec, for the supply
> rail to reach the target voltage, plus/minus whatever tolerance the
> board design requires, once the regulator output itself has ramped up.
> This value is in addition to whatever built-in ramp time is inherent in
> the regulator's own internal design or configuration. This property
> describes the additional ramp time required due to board design issues
> such as trace capacitance and load on the supply.
>
> That's text repeats "additional" a bit, but I think describes the
> situation correctly?

I wanted to provide the absolute delay rather than additional delay on 
top of inherit delay from device.

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