Re: [PATCH v2 5/8] dt-bindings: mfd: axp20x: Add software based soft_start for AXP209 LDO3

From: Lee Jones
Date: Fri Dec 21 2018 - 03:40:17 EST

On Tue, 11 Dec 2018, Priit Laes wrote:

> From: Olliver Schinagl <oliver@xxxxxxxxxxx>
> 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@xxxxxxxxxxx>
> Signed-off-by: Priit Laes <plaes@xxxxxxxxx>
> ---
> Documentation/devicetree/bindings/mfd/axp20x.txt | 3 +++
> 1 file changed, 3 insertions(+)

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

Lee Jones [æçæ]
Linaro Services Technical Lead â Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog