printk: Allow printk_trigger_flush() to flush all types

Currently printk_trigger_flush() only triggers legacy offloaded
flushing, even if that may not be the appropriate method to flush
for currently registered consoles. (The function predates the
NBCON consoles.)

Since commit 6690d6b ("printk: Add helper for flush type
logic") there is printk_get_console_flush_type(), which also
considers NBCON consoles and reports all the methods of flushing
appropriate based on the system state and consoles available.

Update printk_trigger_flush() to use
printk_get_console_flush_type() to appropriately flush registered
consoles.

Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/stable/20251113160351.113031-2-john.ogness%40linutronix.de
Tested-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://patch.msgid.link/20251113160351.113031-2-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>

Author: jogness

kernel/printk/nbcon.c

@@ -1849,7 +1849,7 @@ void nbcon_device_release(struct console *con)
 			if (console_trylock())
 				console_unlock();
 		} else if (ft.legacy_offload) {
-			printk_trigger_flush();
+			defer_console_output();
 		}
 	}
 	console_srcu_read_unlock(cookie);

kernel/printk/printk.c

@@ -4567,9 +4567,30 @@ void defer_console_output(void)
 	__wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
 }
 
+/**
+ * printk_trigger_flush - Attempt to flush printk buffer to consoles.
+ *
+ * If possible, flush the printk buffer to all consoles in the caller's
+ * context. If offloading is available, trigger deferred printing.
+ *
+ * This is best effort. Depending on the system state, console states,
+ * and caller context, no actual flushing may result from this call.
+ */
 void printk_trigger_flush(void)
 {
-	defer_console_output();
+	struct console_flush_type ft;
+
+	printk_get_console_flush_type(&ft);
+	if (ft.nbcon_atomic)
+		nbcon_atomic_flush_pending();
+	if (ft.nbcon_offload)
+		nbcon_kthreads_wake();
+	if (ft.legacy_direct) {
+		if (console_trylock())
+			console_unlock();
+	}
+	if (ft.legacy_offload)
+		defer_console_output();
 }
 
 int vprintk_deferred(const char *fmt, va_list args)