Subject: Re: [PATCH V4 1/6] dt-bindings: regulator: Add
 "regulator-min-dropout-voltage-microvolt"
To:     Mark Brown <broonie@kernel.org>
CC:     Bjorn Andersson <bjorn.andersson@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Liam Girdwood <lgirdwood@gmail.com>, <swboyd@chromium.org>,
        <collinsd@codeaurora.org>, <subbaram@codeaurora.org>,
        Das Srinagesh <gurus@codeaurora.org>,
        <linux-arm-msm@vger.kernel.org>,
        "Lee Jones" <lee.jones@linaro.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
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 <YZ+o9sQpECZSrieN@sirena.org.uk>
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 <Ya5VhkggWdjYyTHL@sirena.org.uk>
From:   "Satya Priya Kakitapalli (Temp)" <quic_c_skakit@quicinc.com>
Message-ID: <6a44cb99-6894-c9ce-4f1e-5dee0939598c@quicinc.com>
Date:   Tue, 7 Dec 2021 20:36:11 +0530
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On 12/6/2021 11:55 PM, Mark Brown wrote:
> On Mon, Dec 06, 2021 at 06:33:26PM +0530, Satya Priya Kakitapalli (Temp) wrote:
>> On 11/25/2021 8:47 PM, Mark Brown wrote:
>>> Usually this is a fixed property of the regulator rather than something
>>> that varies per board - why have a DT property?
>> The min-dropout value (headroom) varies with boards, that's why we have a DT
>> property for it. We overwrite the default value in driver with actual value
>> read from DT
> Interesting.  How exactly does that end up happening - presumably other
> systems are going to run into it?


The parent supplies such as "vdd-l1-l2" are coming from other pmic 
regulators, which are shared supplies with other subsystems like BT, 
Display etc, they vary between boards as per requirements, so we cannot 
expect these to be fixed and so are the headroom values. We get the 
headroom values from PMIC systems team for every target.


> If you do have board designs which somehow managed to introduce
> additional dropouts (seems pretty concerning TBH) then I think the best
> way to handle that is to add a generic property for it and have that
> either added on to or override the requirements of the regulator itself
> which should continue to be defined in the driver.  That way only boards
> with issues need to do anything which will avoid bugs with the property
> being omitted in what should be the common case.