[doc] Remove requirement to enable/disable CSRNG and ENTROPY_SRC in sync

This requirement got added by c6d92ff
and was required as the handshake interfaces between previous versions
of ENTROPY_SRC and CSRNG were erroneously not stateless (for details,
see #17941). This issue got fixed before the
Earlgrey production tapeout (see #21787). In the
meantime, it has been successfully verified on silicon that ENTROPY_SRC
can be disabled/re-enabled while CSRNG remains running. However, the
interfaces between CSRNG and the EDNs are still not stateless and
therefore, the EDNs can only be disabled and re-enabled together with
CSRNG.

This resolves #26779.

Signed-off-by: Pirmin Vogel <[email protected]>
(cherry picked from commit ba2e732)

Author: vogelpi

hw/ip/csrng/doc/programmers_guide.md

@@ -4,9 +4,9 @@ This section discusses how software can interface with CSRNG.
 
 ## Module enable and disable
 
-CSRNG may only be enabled if `ENTROPY_SRC` is enabled.
 CSRNG may only be disabled if all EDNs are disabled.
-Once disabled, CSRNG may only be re-enabled after `ENTROPY_SRC` has been disabled and re-enabled.
+
+The recommended enable sequence for the entropy complex is to first enable ENTROPY_SRC, then CSRNG, and finally the EDNs.
 
 ## Endianness and Known-Answer Tests
 

hw/ip/entropy_src/doc/programmers_guide.md

@@ -20,8 +20,6 @@ Since there exists another feature to avoid power spikes between ENTROPY_SRC and
 Bit 16 in the [`DEBUG_STATUS`](registers.md#debug_status) should be polled after the ENTROPY_SRC enable bits are cleared in the [`CONF`](registers.md#conf) register.
 After the handshakes with CSRNG are finished, the above bit should be set and the ENTROPY_SRC block can be safely enabled again.
 
-ENTROPY_SRC may only be disabled if CSRNG is disabled.
-
 Disabling Entropy Source does not clear the bits in `RECOV_ALERT_STS` (see [*Handling a Recoverable Alert*](#handling-a-recoverable-alert)).