lib/fw_config: Add mainboard hook for selective probe override

Add fw_config_probe_mainboard_override() hook that allows mainboards
to selectively override specific fw_config probes. The hook returns
whether the function handed the probe or not. If set to true, the
hook's 'result' parameter is returned; otherwise, standard fw_config
logic is used automatically.

This enables mainboards to override probes based on runtime conditions
(e.g., CFR options) without reimplementing standard fw_config logic.
The change is backward compatible as the default hook doesn't handle
any probes.

TEST=tested with subsequent patch

Change-Id: I6b9207eb9097ef5296fb5c41d8d1acbfde68b445
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/90741
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/include/fw_config.h

@@ -71,6 +71,20 @@ static inline bool fw_config_is_provisioned(void)
  */
 uint64_t fw_config_get_field(const struct fw_config_field *field);
 
+/**
+ * fw_config_probe_mainboard_override() - Mainboard hook to override specific probes
+ * @match: Structure containing field and option to probe
+ * @result: Output parameter - set to the probe result if this probe was handled
+ *
+ * Return: %true if this probe was handled, %false otherwise
+ *
+ * Mainboards can override this function to handle specific fw_config probes
+ * (e.g., based on CFR/CMOS options). If a probe is handled, return %true and
+ * set *result to the desired probe result. If not handled, return %false and
+ * the standard fw_config logic will be used.
+ */
+bool fw_config_probe_mainboard_override(const struct fw_config *match, bool *result);
+
 /**
  * fw_config_probe() - Check if field and option matches.
  * @match: Structure containing field and option to probe.

src/lib/fw_config.c

@@ -72,8 +72,19 @@ uint64_t fw_config_get_field(const struct fw_config_field *field)
 	return value;
 }
 
+bool __weak fw_config_probe_mainboard_override(const struct fw_config *match, bool *result)
+{
+	return false;
+}
+
 bool fw_config_probe(const struct fw_config *match)
 {
+	bool result;
+
+	/* Give mainboard a chance to override this probe */
+	if (fw_config_probe_mainboard_override(match, &result))
+		return result;
+
 	/* If fw_config is not provisioned, then there is nothing to match. */
 	if (!fw_config_is_provisioned())
 		return false;