Hey all,

Sorry for top-posting, but I did not want to break the thread, while the initial mail does provide background information.

So I've implemented a software-based soft-start in the regulator_enable function of the axp209. This works as expected. Whether it is the right solution I'll happily debate with the patch-set I'm about to send.

The question that remains however, is how is voltage ramping supposed to work?

Right now, the core checks and setups various constraints. Two which are somewhat in conflicting order are:

regulator-always-on

and

ramp-delay.

If, for reasons outside of our control the regulator was not on during boot (miss-configured u-boot) but we want it to be always-on from the kernel side of things, we run into a problem, because the kernel turns the regulator on first (because of regulator-always-on) and only then sets its constraints.

Now we could in our specific case, tell the driver to check for the ramp-delay constraint, and then run it during init/probe, but that feels a little bit like a hack.

So my question is, what is there against moving some of the constrants before the always-on, so that the enable can atleast function properly according to its parameters?

Olliver

On 01-03-17 14:58, Olliver Schinagl wrote:
Hey all,

We found a bug in the design of a board that we use. This board (Olimex
OLinuXino Lime2) features a PMIC (AXP209) and has an LDO, LDO3, that
needs special treatment.

The bug is, that there is too much capacitance on the output of LDO3,
which causes the PMIC to shutdown when enabeling LDO3.

The AXP does have voltage ramp control for LDO3, but this is only
effective After LDO3 has been enabled.

To be able to turn on LDO3, we have to first set its voltage to the
lowest setting (0.7 V), wait 1 ms, then turn it on. After that the
voltage can be changed normally.

I'm already working on the patches to add the voltage ramp control but
as described above, this will not fix the problem here.

My guess, and hence the question, is that we will need to add support
for this quirk in the AXP209 LDO3 enable case. There are no quirk flags
that I could find yet, so how is this preferabbly handled? A board level
flag in the dts? AXP-level flag? Or is the soft-start flag sort of
inteded for this? e.g. set soft-start for ldo3 in the dts, check this
flag in the enable function and do the earlier described start-up?

Thanks,

Olliver

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