linux-kernel - Re: [PATCH v5 6/6] regulator: core: Prevent falling too fast

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Date:   Fri, 23 Sep 2016 10:16:25 -0500
From:   Rob Herring <robh@...nel.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Mark Brown <broonie@...nel.org>, lgirdwood@...il.com,
        Douglas Anderson <dianders@...omium.org>,
        briannorris@...omium.org, javier@...hile0.org,
        mark.rutland@....com, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v5 6/6] regulator: core: Prevent falling too fast

On Wed, Sep 14, 2016 at 09:52:10AM -0700, Matthias Kaehlcke wrote:
> From: Douglas Anderson <dianders@...omium.org>
> 
> On some boards it is possible that transitioning the regulator downwards
> too fast will trigger the over voltage protection (OVP) on the
> regulator. This is because until the voltage actually falls there is
> time when the requested voltage is much lower than the actual voltage.
> 
> We'll fix this OVP problem by allowing users to specify the maximum
> voltage that we can safely fall. The maximum safe voltage decrease
> is specified as a percentage of the current voltage. The driver will
> then break things into separate steps with a delay in between.
> 
> In order to figure out what the delay should be we need to figure out
> how slowly the voltage rail might fall in the worst (slowest) case.
> We'll assume this worst case is present and delay so we know for sure
> that we've finished each step.
> 
> In this patch we actually block returning from the set_voltage() call
> until we've finished delaying. A future patch atop this one might
> choose to return more immediately and let the voltages fall in the
> background. That would possibly allow us to cancel a slow downward
> decay if there was a request to go back up.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> ---
> Changes in v5:
> - Leave set_voltage tracepoints where they were
> - Fixed error handling in code dealing with the device tree, return an error if configuration is invalid
> - Fixed coding style and formatting issues
> - Updated commit message
> 
>  .../devicetree/bindings/regulator/regulator.txt    |  7 ++++

For the binding:

Acked-by: Rob Herring <robh@...nel.org>

>  drivers/regulator/core.c                           | 49 +++++++++++++++++++---
>  drivers/regulator/of_regulator.c                   | 42 ++++++++++++++++++-
>  include/linux/regulator/machine.h                  |  2 +
>  4 files changed, 93 insertions(+), 7 deletions(-)