linux-kernel - Re: [PATCH v3 01/11] regulator: core: add API to get voltage constraints

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Date:   Wed, 7 Feb 2018 16:32:13 +0200
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Mark Brown <broonie@...nel.org>
CC:     <linux-tegra@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <mturquette@...libre.com>, <sboyd@...eaurora.org>,
        <robh+dt@...nel.org>, <mark.rutland@....com>,
        <devicetree@...r.kernel.org>, <lgirdwood@...il.com>,
        <linux-kernel@...r.kernel.org>,
        Laxman Dewangan <ldewangan@...dia.com>
Subject: Re: [PATCH v3 01/11] regulator: core: add API to get voltage
 constraints

On Wed, Feb 07, 2018 at 02:18:46PM +0000, Mark Brown wrote:
> On Wed, Feb 07, 2018 at 02:37:51PM +0200, Peter De Schrijver wrote:
> > On Wed, Feb 07, 2018 at 10:43:51AM +0000, Mark Brown wrote:
> > > On Wed, Feb 07, 2018 at 10:47:44AM +0200, Peter De Schrijver wrote:
> > > > On Tue, Feb 06, 2018 at 04:35:44PM +0000, Mark Brown wrote:
> > > > > On Tue, Feb 06, 2018 at 06:34:02PM +0200, Peter De Schrijver wrote:
> 
> > > > > > Add API to get min/max rail voltage configured from platform for
> > > > > > given rails.
> 
> > > > > because...
> 
> > > > of the next patch where this is used to retrieve the minimum rail voltage.
> 
> > > And that in turn is needed for...?
> 
> > To calculate the required voltage for each frequency.
> 
> You're going to have to provide a much better explanation of what this
> is doing - right now it seems like an abuse of constraints.  Client
> drivers can already determine if a particular voltage they want to set
> is available via regulator_list_voltage() and so on, that's what
> constraints are there to set.  It sounds like you're trying to use them
> for something else but you're really not explaining your use case
> clearly.

There is no way to query what voltage I will actually get for a given input
voltage. If you read drivers/clk/tegra/cvb. (you did do that right?), you
will see that there is a minimum and maximum voltage defined by
charaterization which needs to be capped to the regulator generated voltages
for those points.

Peter.