[Letux-kernel] weird problem with pwm_bl on omap3

[H. Nikolaus Schaller]

Hi,

> Am 29.05.2018 um 21:15 schrieb Andreas Kemnade <andreas at kemnade.info>:
> 
> Hi,
> 
> On Tue, 29 May 2018 18:36:05 +0200
> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
> 
>> Hi Andreas,
>> 
>>> Am 29.05.2018 um 18:27 schrieb Andreas Kemnade <andreas at kemnade.info>:
>>> 
>>> On Tue, 29 May 2018 17:41:53 +0200
>>> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
>>> 
>>>> Hi Tony,
>>>> 
>>>>> Am 17.05.2018 um 20:08 schrieb Tony Lindgren <tony at atomide.com>:
>>>>> 
>>>>> * H. Nikolaus Schaller <hns at goldelico.com> [180517 12:17]:
>>>>>> Hi Tony,
>>>>>> we are using for long time the dmtimer/pwm on
>>>>>> the GTA04 to drive the display panel backlight.
>>>>>> 
>>>>>> Starting a while ago (I am not sure when, but it may
>>>>>> be 4.17-rc1), the device randomly fails to boot
>>>>>> with a NULL pointer dereference in strcmp().
>>>>>> Booting again usually runs fine.
>>>>> 
>>>>> Hmm maybe enable CONFIG_DEBUG_SLAB=y and POISON options
>>>>> and see if that catches something. It's might be some
>>>>> array out of bounds type issue.
>>>>> 
>>>>> Regards,
>>>>> 
>>>>> Tony
>>>> 
>>>> 
>>>> I have restarted hunting the issue but it is very
>>>> ghostly. Every time I try to test by another method
>>>> it disappears and if I remove my printk things or
>>>> /etc/modprobe/blacklist.conf it comes back.
>>>> 
>>> Have you tried to load every module piece by piece before running udev
>>> by booting the kernel with a init=/something.sh script?
>>> So you have the order under control?
>> 
>> Well, if I load modules manually everything is fine.
>> The problem appears to be the concurrency of loading
>> and deferred probing of modules.
>> 
>> If I block pwm_bl and omap3dss and some others and load
>> them all manually, there was never a problem :(
>> 
>>> 
>>> Another thing: Are our fb patches evil again?
>> 
>> It also occurs with omapdss blacklisted.
>> 
>>> 
>>> The offmode patch? Maybe it uncovers some other bug.
>> 
>> Hm. I am not sure if I have included it. I am running with
>> mainline with just a handful of our recent patches (not
>> everything).
>> 
>> But I can try it as soon as I find time (kernel compiling has
>> got much slower in recent years so that I have new ideas
>> faster than a test result :).
>> 
>>> 
>>> Just to sort out some non-mainline stuff
>>> 
>>> I am compiling and will try to boot with my scripts this evening.
>> 
>> Yes, please. At least to check if you can observe the same issue.
>> It seems to happen more often on a GTA04A5 that a GTA04A4.
>> 
> Reproducible with letux-4.17-rc5

Good (even if bad :)

> not reproducible with  mainline 4.17-rc7 + letux-4.17-rc5 dtb

Well, they do not have all the drivers we need...
And/or there may be different timing for probe activities.

Which defconfig did you use?

BR and thanks,
Nikolaus

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