Power button behaviour

[Andy Green]

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Somebody in the thread at some point said:

| What is correct :
|
| 1/ There is no more power-management chip for hardware reset chip in
| GTA02 ? Why ?
| 2/ The kernel configures the power-management chip at boot, and then
| only, the hardware reboot is working
|
| If 1 is true, does this mean it's not sure we can power off a zombified
| kernel system ( ugly battery removal procedure )?
| If 2 is true, can we  move the  power-management chip initialization in
| bootloader so it works as soon as possible in boot sequence?

The "PMU is boss of our boards" for both GTA01 and GTA02.  On the
pcf50606 PMU in GTA01 as mwester said it listens out for button held and
takes action itself.

On pcf50633 on GTA02, whether it will listen for power button hold or
not is determined by which "variant" you bought from NXP.  On the one
that is closest to what we would want, it is told to not listen.  And
unusually, that behaviour is not changeable over I2C at all, it is
permanently and solely decided by which type you got from NXP.

It means all we can do is partially synthesize the behaviour in the
driver, which doesn't help if the CPU is crashed.

There were only a couple of real choices about PMU variant, we made the
best choice all things considered and this behaviour is a small breakage
we have to accept to get the rest of the reasonable matches on other
behaviour -- it isn't the only ding we have to take to balance heaven
and earth with the PMU.

- -Andy
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