[Letux-kernel] weird problem with pwm_bl on omap3

[Andreas Kemnade]

On Tue, 29 May 2018 21:55:52 +0200
"H. Nikolaus Schaller" <hns at goldelico.com> wrote:

> 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.
>
well, by putting modprobe into a script we could find out something.
 
> Which defconfig did you use?

It is just the ordinary letux_defconfig. after compiling and before
doing anything with mainline I do a backup of the generated config.
I just did a make oldconfig after checking out mainline.

Regards,
Andreas
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