linux-kernel - Re: [PATCH v2 5/8] dt-bindings: mfd: axp20x: Add software based soft

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Date:   Fri, 21 Dec 2018 08:40:10 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Priit Laes <plaes@...es.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Chen-Yu Tsai <wens@...e.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Olliver Schinagl <oliver@...inagl.nl>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH v2 5/8] dt-bindings: mfd: axp20x: Add software based
 soft_start for AXP209 LDO3

On Tue, 11 Dec 2018, Priit Laes wrote:

> From: Olliver Schinagl <oliver@...inagl.nl>
> 
> In the past, there have been words on various lists that if LDO3 is
> disabled in u-boot, but enabled in the DTS, the axp209 driver would
> fail to continue/hang. Several enable/disable patches have been
> issues to devicetree's in both the kernel and u-boot to address
> this issue.
> 
> What really happened however, was that the AXP209 shuts down without
> a notice and without setting an interrupt. This is caused when LDO3
> gets overloaded, for example with large capacitors on the LDO3 output.
> 
> Normally, we would expect that AXP209 would source 200 mA as per
> datasheet and set and trigger an interrupt when being overloaded.
> For some reason however, this does not happen.
> 
> As a work-around, implement software-based 'regulator-soft-start'
> property for AXP209 LDO3 regulator, which is used to first bring up
> the LDO3 to the lowest possible voltage and then enable the LDO.
> 
> After that, we can set the requested voltage as usual.
> 
> Combining this setting with the regulator-ramp-delay allows LDO3 to
> come up slowly and staggered, potentially reducing overall inrush current.
> 
> Signed-off-by: Olliver Schinagl <oliver@...inagl.nl>
> Signed-off-by: Priit Laes <plaes@...es.org>
> ---
>  Documentation/devicetree/bindings/mfd/axp20x.txt | 3 +++
>  1 file changed, 3 insertions(+)

For my own reference:
  Acked-for-MFD-by: Lee Jones <lee.jones@...aro.org>

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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