jitterentropy_rng on armv5 embedded target

[Alexander Dahl <ada@thorsis.com>]

Hello,

after upgrading OpenSSL to 1.1.1g on an armv5 based embedded target I had a 
deeper look into entropy generation for that device and stumbled over the in 
kernel 'jitterentropy_rng' module.

As far as I understood it's supposed to do the same as the well known 
'haveged' or the userspace daemon 'jitterentropy-rngd' by Stephan Müller [1], 
right? (Although those daemons would solve my problem, I currently try to 
avoid them, because memory on my platform is very restricted and every 
additional running userspace process costs at least around 1 MB.)

If so, then how is it supposed to be set up? I built it for 4.9.x LTS, but 
after loading it with 'modprobe' I see nothing in the kernel log and there's 
no significant change in /proc/sys/kernel/random/entropy_avail (stays well 
below 100 most of the time). Isn't that module supposed to gather entropy from 
cpu timing jitter?

Puzzled
Alex

[1] https://www.chronox.de/jent.html