cbfs: Add a function to wait for all CBFS preload operations to complete

Introduce cbfs_preload_wait_for_all() to guarantee that all CBFS preload
contexts complete their tasks before moving forward. This function goes
through each preload context and waits for the corresponding thread to
finish by using thread_join(). If any preload thread runs into an issue,
it records an error message along with the context name.

This addition provides a synchronization point during the boot process
which platform code can leverage, typically when the storage backend
supporting asynchronous file transfer is about to be deactivated.

Change-Id: I3ee27ef2fbfdc19bd75532713966f333ad975861
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/88457
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/cbfs.h

@@ -126,6 +126,8 @@ static inline void *cbfs_unverified_area_cbmem_alloc(const char *area, const cha
  * method succeeds or fails.
  */
 void cbfs_preload(const char *name);
+/* Wait for all preloaded CBFS contexts to complete their operations. */
+void cbfs_preload_wait_for_all(void);
 
 /* Removes a previously allocated CBFS mapping. Should try to unmap mappings in strict LIFO
    order where possible, since mapping backends often don't support more complicated cases. */

src/lib/cbfs.c

@@ -376,6 +376,14 @@ out:
 	free_cbfs_preload_context(context);
 }
 
+void cbfs_preload_wait_for_all(void)
+{
+	struct cbfs_preload_context *context;
+
+	list_for_each(context, cbfs_preload_context_list, list_node)
+		thread_join(&context->handle);
+}
+
 static struct cbfs_preload_context *find_cbfs_preload_context(const char *name)
 {
 	struct cbfs_preload_context *context;