[entropy_src,csrng,edn] Features for next version / future releases of entropy complex

[vogelpi]

Description

When working towards Earlgrey-PROD and during the SiVal work, we had many constructive discussions regarding how the entropy complex works and what additional features are currently missing / could be relevant in the future / would be nice to have. The idea of this issue is to keep track of such potential future features and link to the corresponding discussions in one shared place for later reference.

ENTROPY_SRC:

• Consider adding support for testing the hardware health tests on the chip, e.g., with a hardware interface that allows feeding known values into the health tests. See [entropy_src] Need support for testing health tests #22289.
• Consider adding an option to not clear the esfinal FIFO upon disabling and keep serving previously produced seeds to CSRNG when disabled. This could help to save power as the ENTROPY_SRC (and RNG) can remain disabled for a longer period. See [ast, entropy_src] Reducing idle power #22223.
• Consider replacing the ES_ROUTE switch by a CSR triggering only the next seed becoming software readable while other seeds continue propagating to the hardware interface. See [entropy_src] Enabling ENTROPY_DATA prevents CSRNG from getting entropy #23947.

CSRNG:

• Add support for greater seed lengths, e.g., by using derivation functions. See [csrng] input seed length shall be larger than 384 bits #22157 and [cryptolib] support for EC key generation from provided DRBG #21936.
• Based on real measurements, decide whether it would make sense to implement something to prevent reseed operations blocking other instances. See [csrng] Future improvement for reseed blocking #14505.
• Return a status error for Generate commands with a generate length = 0, see [csrng] Return error status response for GEN commands with glen = 0 #23846.
• ...

EDN:

• Add support for tracking the frequency of requests produced by individual end points. This would simplify debugging power issues. See [edn] Investigate why there are many EDN requests after ROM_EXT #22819.
• ...