linux-kernel - Re: [PATCH v4 1/2] regulator: dt-bindings: add QCOM RPMh regulator bindings

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Date:   Wed, 30 May 2018 17:34:43 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     David Collins <collinsd@...eaurora.org>
Cc:     Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-msm@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        devicetree@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephen Boyd <sboyd@...nel.org>
Subject: Re: [PATCH v4 1/2] regulator: dt-bindings: add QCOM RPMh regulator bindings

Hi,

On Wed, May 30, 2018 at 4:39 PM, David Collins <collinsd@...eaurora.org> wrote:
> Consider the case of a regulator with physical 10 mA LPM max current. Say
> that modem and application processors each have a load on the regulator
> that draws 9 mA. If they each respect the 10 mA limit, then they'd each
> vote for LPM. The VRM block in RPMh hardware will aggregate these requests
> together using a max function which will result in the regulator being set
> to LPM, even though the total load is 18 mA (which would require high
> power mode (HPM)). To get around this corner case, a LPM max current of 1
> uA can be used for all LDO supplies that have non-application processor
> consumers. Thus, any non-zero regulator_set_load() current request will
> result in setting the regulator to HPM (which is always safe).

Is there any plan to change the way this works for future versions of RPMh?


> The second situation that needs board-level DRMS mode and current limit
> specification is SMPS regulator AUTO mode to PWM (HPM) mode switching.
> SMPS regulators should theoretically always be able to operate in AUTO
> mode as it switches automatically between PWM mode (which can provide the
> maximum current) and PFM mode (which supports lower current but has higher
> efficiency). However, there may be board/system issues that require
> switching to PWM mode for certain use cases as it has better load
> regulation (i.e. no PFM ripple for lower loads) and supports more
> aggressive load current steps (i.e. greater A/ns).
>
> If a Linux consumer requires the ability to force a given SMPS regulator
> from AUTO mode into PWM mode and that SMPS is shared by other Linux
> consumers (which may be the case, but at least must be guaranteed to work
> architecturally), then regulator_set_load() is the only option since it
> provides aggregation, where as regulator_set_mode() does not.
> regulator_set_load() can be utilized in this case by specifying AUTO mode
> and PWM mode as drms modes and specifying some particular AUTO mode
> maximum current (that is known by the consumer) in device tree.  The
> consumer can then call regulator_set_load() with the imposed AUTO mode
> limit + delta when PWM mode is required and a lower value when AUTO mode
> is sufficient.

Mark: I'm leaving this firmly in your hands.  I can see David's points
here.  I could even believe that some of this stuff could be board
specific where one board might have slightly different capacitors or
they might be placed differently and might need a higher power mode to
keep the signal clean.

-Doug