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

[H. Nikolaus Schaller]

Hi,
small addendum - there must be another factor involved.

> Am 11.09.2018 um 20:20 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> 
>> Am 11.09.2018 um 18:26 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
>> 
>> Hi,
>> 
>>> Am 11.09.2018 um 15:07 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
>>> 
>>> Hi Tero,
>>> 
>>> After kernel has booted, there is a single difference
>>> in CM_ABE_CLKSTCTRL.
>>> 
>>> The relevant bit is: CLKACTIVITY_DPLL_ABE_X2_CLK
>>> 
>>> After reboot, there are bigger differences not wiped
>>> out by u-boot.
>>> 
>>> So the question is what disturbs this clock,
>>> especially as CLKACTIVITY_DPLL_ABE_X2_ seems
>>> to say that the clock is active (on Pyra) but
>>> not on EVM (I had expected the reverse to be more
>>> likely).
>>> 
>>> CM_ABE_CLKSTCTRL remains 0x803 on Pyra and 0x3 on EVM
>> 
>> Well, if we see the same setup by U-Boot after power-on
>> it must be kernel + DTS. Or is this a false conclusion?
>> 
>> So I started to deconfigure kernel subsystems completely:
>> 
>> 1. all twl6040 / abe / aess
>> 2. all OMAP3 & OMAP4
>> 3. all wireless (wl1837 uses some external functional clocks)
>> 4. all sound
>> 
>> And I have checked U-Boot and DTS sources but did not find
>> Pyra specific overwrites for any system clock or abe or dpll
>> related registers.
>> 
>> Then I did rm /lib/modules (the most critical ones are configured
>> into the kernel so that I can still boot), and interestingly the
>> CLKACTIVITY_DPLL_ABE_X2_CLK is now the same (0x3) on Pyra and
>> OMAP5EVM. And "reboot" works.
>> 
>> So I can now simply modprobe blacklist them one after the other
>> to find out which one is conflicting.
> 
> Bingo!
> 
> root at letux:~# more /etc/modprobe.d/blacklist.conf 
> blacklist pwm_omap_dmtimer
> root at letux:~#
> 
> makes the problem go away.
> 
> 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.

> 
> Why don't you see this on omap5uevm even if these modules
> are loaded? I assume there is usually no panel connected
> that makes use of pwm_bl and pwm_omap_dmtimer. And there is
> no compatible = "ti,omap-dmtimer-pwm"; in omap5-board-common.dtsi
> or omap5-uevm.dts. This is a hardware difference between Pyra
> and OMAP5EVM.
> 
> So I think it is now up to you to help me to find out why
> pwm_omap_dmtimer can influence the dpll_abe_ck...
> 
> BR and thanks,
> Nikolaus
> 
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