[PATCH 4/5] staging: vchiq_arm: Create keep-alive thread during probe

[MichaIng]

 > Okay, after disabling all VCHIQ users including VCHIQ_CDEV and 
enabling DETECT_HUNG_TASK, i was able to reproduce it.

 > I will try to fix that.

Hi Stefan,

is there any progress in this regards, or a way we can help? Would it 
make sense to share the issue to the RPi Ltd. downstream repository?
https://github.com/raspberrypi/linux

We ship images with downstream RPi Ltd. kernel packages, but with 
non-GUI/server setups and low memory usage in mind, we disable/blacklist 
camera and GPU related kernel modules by default, and reduce the 
dedicated GPU memory to the minimal 16 MiB, so that our users report as 
well these errors every few minutes on their main console, until GUI, 
video codec, or camera features are enabled.

I am thinking about letting one kernel module load by default which 
releases the hanging task. But the majority of systems are headless, and 
really don't require any of those. Reducing the console log level or 
muting hung task timeout messages would be another workaround, but that 
could mute important messages as well.

Just in case someone else is in the same situation: I found the VC CMA 
driver "vc_sm_cma" module to be the lightest way of releasing the 
waiting task. Other than the camera/video modules, it does not pull in a 
large stack of dependency modules. With less than 32 MiB GPU memory 
(where the cut-down firmware is used automatically), it fails to 
initialise, but releases the vchiq-keep thread regardless. Its size is 
also tiny compared to the Broadcom camera/video drivers.

-- 
Best regards,

Micha (aka MichaIng)
DietPi project lead