On Wed, Nov 21, 2018 at 08:05:31PM +0200, Priit Laes wrote:
From: Olliver Schinagl oliver@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@schinagl.nl Signed-off-by: Priit Laes plaes@plaes.org
Acked-by: Maxime Ripard maxime.ripard@bootlin.com
Maxime