[Letux-kernel] OMAP5: Debugging kernel not starting... (and clock: dpll_abe_ck failed transition to 'locked')

H. Nikolaus Schaller hns at goldelico.com
Wed Sep 12 18:17:26 CEST 2018

Hi Tony,

> Am 12.09.2018 um 02:03 schrieb Tony Lindgren <tony at atomide.com>:
> * H. Nikolaus Schaller <hns at goldelico.com> [180911 18:28]:
>>> BTW: blacklisting pwm_bl makes CLKACTIVITY_DPLL_ABE_X2_CLK
>>> show the right value but reboot still can't transition
>>> dpll_abe_ck to 'locked'.
>> After adding back all modules except pwm_omap_dmtimer the problem
>> comes back to the Pyra. And adding a omap-dmtimer-pwm to the omap5-uevm.dts
>> does make CLKACTIVITY_DPLL_ABE_X2_CLK become 0x803 as I see on the
>> Pyra, but it still handles reboots properly.
>> More test results to come tomorrow.
> OK good to hear you got it narrowed down.

I have further narrowed it down to

root at letux:~# more /etc/modprobe.d/pwm.conf 
blacklist pwm_omap_dmtimer
blacklist snd_soc_omap_abe_twl6040
root at letux:~#

which always reboots fine (tested with letux-4.18.7 and 4.19-rc1 and 4.14.58).


	modprobe pwm_omap_dmtimer

OR (!)

	modprobe snd_soc_omap_abe_twl6040

before "reboot" makes the Pyra boot hang with the dpll_abe_ck failure.

Generally it reminds me a little of the pinctrl and generic-adc-battery
drivers problem where it turned out that the main problem was a write-out-of-bounds
in generic-adc-battery so that it did occur only if drivers were loaded in a
specifc sequence.

But this here is more reproducible. On the Pyra.

I am still trying to reproduce the effect on the omap5evm by amending
the mainline DTS. It does reboot with these modules loaded...

What I alread wonder is what

- dpll_abe_ck setup
- pwm_omap_dmtimer
- snd_soc_omap_abe_twl6040

have in common so that they can influence each other?

hwmods? clock setup? dividers? plls?


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