[Letux-kernel] weird problem with pwm_bl on omap3

[Andreas Kemnade]

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

Regards,
Andreas
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