[U-Boot] [PATCH v3 7/9] power: axp209: Limit inrush current for broken boards

[Maxime Ripard]

On Wed, Nov 21, 2018 at 08:05:31PM +0200, Priit Laes wrote:
> From: Olliver Schinagl <oliver at schinagl.nl>
> 
> Some boards feature a capacitance on LDO3's output that is too large,
> causing inrush currents which as a result, shut down the AXP209. This
> has been reported before, without knowing the actual cause.
> 
> A fix appeared to be done with
> commit 0e6e34ac8dbb ("sunxi: Olimex A20 boards: Enable LDO3 and LDO4 regulators").
> 
> The description there is a bit misleading, the kernel does not hang
> during AXP209 initialization, the PMIC shuts down, causing voltages to
> drop and thus the whole system freezes.
> 
> While the AXP209 does have the ability to ramp up the voltage slowly, to
> reduce these inrush currents, the voltage rate control (VRC) however is
> not applicable when switching on the LDO3 output. Only when going from
> an enabled lower voltage setting, to a higher voltage setting is the VRC
> in effect.
> 
> To work around this problem, we set LDO3 to the lowest possible setting
> of 0.7 V if it was not yet enabled, and then let the VRC (if enabled) do
> its thing. It should be noted, that for some undocumented reason, there
> is a short delay needed between setting the LDO3 voltage register and
> enabling the power. One would expect that this delay ought to be just
> after enabling the output power at 0.7 V, but this did not work.
> 
> Signed-off-by: Olliver Schinagl <oliver at schinagl.nl>
> Signed-off-by: Priit Laes <plaes at plaes.org>

Acked-by: Maxime Ripard <maxime.ripard at bootlin.com>

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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