[Letux-kernel] Idle-osc-off questions

Andreas Kemnade andreas at kemnade.info
Mon Feb 26 23:22:09 CET 2018


I am stumbling across another thing I do not understand:

What does this idle-osc-thing really?

If I understand the code correctly,
                .compatible = "ti,twl4030-power-idle-osc-off",

enables this part of the sleep script (in twl4030-power.c)

which should control the CLKEN pin to power off (tps65950 TRM p. 238)
the oscillator. But CLKEN is not connected.

Then there is the comment in the source
/* Disable 32 KiHz oscillator during idle */

which does not make sense. Disabling a 32khz osc?
Especially since rtc wakeup works.

Looking at the changes in the schematic, I see that the enable
pin of that 26Mhz osc is connected to vpll1. According to this line,

It seems to be switched off in suspend. Switching a 26Mhz osc off when
it is not
needed seems to be sane.
But that rises even more questions.

VPLL1 out is just connected to a capacitor and the oscillator enable
pin. But how is that capacitor discharged? Across leakages in the
oscillator and the internal regulator feedback loop probably. Well,
if we have discharges around 1uA, then it will go down after some time.

But the idle-osc-off thing has influences. 
- some mA lower suspend currents
- strange behaviour on idle currents
  -> sometimes even 6mA below the currents in the same state
     as without idle-osc-off, sometimes up to 20mA higher,
     generally not worse when everything is loaded than without
     that osc-off thing.
- strange behaviour when suspending while charging
   -> immediate wakeup with strange errors.

The behaviour feels like floating pins or some clown has randomly
changed some macro parameter order.
Can someone enlighten me what is going on here?

Very puzzled,
PS: suspend current at 15mA (with modem off and a bit of esoteric)
The thread then continues with a lot of esoteric.
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