`rngd` seems to be the root cause for slow boot issues, and its functionality is
redundant since kernel v3.17 (2014), which introduced a `krngd` task (in kernel
space) that takes care of pulling in data from hardware RNGs:
> commit be4000bc4644d027c519b6361f5ae3bbfc52c347
> Author: Torsten Duwe <duwe@lst.de>
> Date: Sat Jun 14 23:46:03 2014 -0400
>
> hwrng: create filler thread
>
> This can be viewed as the in-kernel equivalent of hwrngd;
> like FUSE it is a good thing to have a mechanism in user land,
> but for some reasons (simplicity, secrecy, integrity, speed)
> it may be better to have it in kernel space.
>
> This patch creates a thread once a hwrng registers, and uses
> the previously established add_hwgenerator_randomness() to feed
> its data to the input pool as long as needed. A derating factor
> is used to bias the entropy estimation and to disable this
> mechanism entirely when set to zero.
Closes: #96067
e64d3f60fb