printk: nbcon: Consolidate alloc() and init()

Rather than splitting the nbcon allocation and initialization into
two pieces, perform all initialization in nbcon_alloc(). Later,
the initial sequence is calculated and can be explicitly set using
nbcon_seq_force(). This removes the need for the strong rules of
nbcon_init() that even included a BUG_ON().

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240820063001.36405-3-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>

kernel/printk/internal.h

@@ -75,7 +75,6 @@ u16 printk_parse_prefix(const char *text, int *level,
 u64 nbcon_seq_read(struct console *con);
 void nbcon_seq_force(struct console *con, u64 seq);
 bool nbcon_alloc(struct console *con);
-void nbcon_init(struct console *con);
 void nbcon_free(struct console *con);
 
 #else
@@ -96,7 +95,6 @@ static inline bool printk_percpu_data_ready(void) { return false; }
 static inline u64 nbcon_seq_read(struct console *con) { return 0; }
 static inline void nbcon_seq_force(struct console *con, u64 seq) { }
 static inline bool nbcon_alloc(struct console *con) { return false; }
-static inline void nbcon_init(struct console *con) { }
 static inline void nbcon_free(struct console *con) { }
 
 #endif /* CONFIG_PRINTK */

kernel/printk/nbcon.c

@@ -929,17 +929,22 @@ update_con:
 }
 
 /**
- * nbcon_alloc - Allocate buffers needed by the nbcon console
+ * nbcon_alloc - Allocate and init the nbcon console specific data
- * @con:	Console to allocate buffers for
+ * @con:	Console to initialize
  *
- * Return:	True on success. False otherwise and the console cannot
+ * Return:	True if the console was fully allocated and initialized.
- *		be used.
+ *		Otherwise @con must not be registered.
  *
- * This is not part of nbcon_init() because buffer allocation must
+ * When allocation and init was successful, the console must be properly
- * be performed earlier in the console registration process.
+ * freed using nbcon_free() once it is no longer needed.
  */
 bool nbcon_alloc(struct console *con)
 {
+	struct nbcon_state state = { };
+
+	nbcon_state_set(con, &state);
+	atomic_long_set(&ACCESS_PRIVATE(con, nbcon_seq), 0);
+
 	if (con->flags & CON_BOOT) {
 		/*
 		 * Boot console printing is synchronized with legacy console
@@ -958,26 +963,6 @@ bool nbcon_alloc(struct console *con)
 	return true;
 }
 
-/**
- * nbcon_init - Initialize the nbcon console specific data
- * @con:	Console to initialize
- *
- * nbcon_alloc() *must* be called and succeed before this function
- * is called.
- *
- * This function expects that the legacy @con->seq has been set.
- */
-void nbcon_init(struct console *con)
-{
-	struct nbcon_state state = { };
-
-	/* nbcon_alloc() must have been called and successful! */
-	BUG_ON(!con->pbufs);
-
-	nbcon_seq_force(con, con->seq);
-	nbcon_state_set(con, &state);
-}
-
 /**
  * nbcon_free - Free and cleanup the nbcon console specific data
  * @con:	Console to free/cleanup nbcon data

kernel/printk/printk.c

@@ -3618,7 +3618,7 @@ void register_console(struct console *newcon)
 	console_init_seq(newcon, bootcon_registered);
 
 	if (newcon->flags & CON_NBCON)
-		nbcon_init(newcon);
+		nbcon_seq_force(newcon, newcon->seq);
 
 	/*
 	 * Put this console in the list - keep the