Clarify the superset rule
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/docs/architecture/psa-migration/transition-guards.md b/docs/architecture/psa-migration/transition-guards.md
index 1193f75..b72abfa 100644
--- a/docs/architecture/psa-migration/transition-guards.md
+++ b/docs/architecture/psa-migration/transition-guards.md
@@ -88,9 +88,11 @@
`MD_LIGHT` is enabled in most builds.)
Note that there is a rule, enforced by `config_adjust_psa_superset_legacy.h`,
-that all hashes that are enabled on the legacy side are also enabled on the
-PSA side. So, in practice, when `MD_LIGHT` is enabled, `PSA_WANT_ALG_xxx` and
-`MBEDTLS_MD_CAN_xxx` are equivalent.
+that as soon as `PSA_CRYPTO_C` is enabled, all hashes that are enabled on the
+legacy side are also enabled on the PSA side (the converse is not true: a hash
+that's provided by a driver will typically be available only on the PSA side). So, in
+practice, when `PSA_CRYPTO_C` and `MD_LIGHT` are both enabled,
+`PSA_WANT_ALG_xxx` and `MBEDTLS_MD_CAN_xxx` are equivalent.
**Legacy and `USE_PSA` domains:** for hashes, `MBEDTLS_MD_CAN_xxx` (where
`xxx` is the legacy name of the hash) can be used everywhere (except in the
@@ -220,9 +222,12 @@
ECC
---
-**Curves:** in `config_adjut_psa_superset_legacy.h` we ensure that all
+**Curves:** in `config_adjut_psa_superset_legacy.h` we ensure that, as soon as
+`PSA_CRYPTO_C` is enabled, all
curves that are supported on the legacy side (`MBEDTLS_ECP_DP_xxx_ENABLED`)
-are also supported on the PSA side (`PSA_WANT_ECC_xxx`).
+are also supported on the PSA side (`PSA_WANT_ECC_xxx`). (The converse is not
+true as a curve provided by a driver will typically only be available on the
+PSA side).
In `config_adjust_legacy_crypto.h` we define macros `MBEDTLS_ECP_HAVE_xxx`.
These macros are useful for data and functions that have users in several