linux-kernel - Re: [RFC v2 5/6] drivers: boot_constraint: Add initial DT bindings

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Message-ID: <20170713050934.GB352@vireshk-i7>
Date:   Thu, 13 Jul 2017 10:39:34 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Shiraz Hashim <shashim@...eaurora.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC v2 5/6] drivers: boot_constraint: Add initial DT bindings

On 13-07-17, 10:52, Chen-Yu Tsai wrote:
> I'm afraid the regulator case still doesn't make sense. The voltage
> constraints should be set within each supplies device node. This was
> explained in the discussion in v1 [1].

I thought we were discussing about something I mentioned in one of my example
but never to a point that the regulator problem doesn't exist at all. Perhaps I
misunderstood your concerns. Anyway, lemme try once more with a better example.

Regulator shared by: LCD and MMC (both can do DVFS) and the min/max constraint
that can be set by the consumers of the regulator (both LCD/MMC) are: 1.5 V to
3 V.

The bootloader has programmed the LCD to work at the highest pixel frequency,
which needs the voltage to be in range from 2.5 - 3 V.

Now MMC can get probed first and it can try to bring the voltages below 2.5 V.
Though, 1.5 - 2.5 is a valid range for the LCD, but not at the current pixel
frequency.

Does that sound like a valid problem?

-- 
viresh