From: John Ogness <john.ogness@linutronix.de>
Date: Mon, 11 Dec 2023 09:36:52 +0000
Subject: [PATCH 114/134] printk: Track nbcon consoles
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz

Add a global flag @have_nbcon_console to identify if any nbcon
consoles are registered. This will be used in follow-up commits
to preserve legacy behavior when no nbcon consoles are registered.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/printk/printk.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -471,6 +471,13 @@ static DEFINE_MUTEX(syslog_lock);
 bool have_legacy_console;
 
 /*
+ * Specifies if an nbcon console is registered. If nbcon consoles are present,
+ * synchronous printing of legacy consoles will not occur during panic until
+ * the backtrace has been stored to the ringbuffer.
+ */
+bool have_nbcon_console;
+
+/*
  * Specifies if a boot console is registered. If boot consoles are present,
  * nbcon consoles cannot print simultaneously and must be synchronized by
  * the console lock. This is because boot consoles and nbcon consoles may
@@ -3523,6 +3530,7 @@ void register_console(struct console *ne
 	console_init_seq(newcon, bootcon_registered);
 
 	if (newcon->flags & CON_NBCON) {
+		have_nbcon_console = true;
 		nbcon_init(newcon);
 	} else {
 		have_legacy_console = true;
@@ -3584,6 +3592,7 @@ EXPORT_SYMBOL(register_console);
 static int unregister_console_locked(struct console *console)
 {
 	bool found_legacy_con = false;
+	bool found_nbcon_con = false;
 	bool found_boot_con = false;
 	struct console *c;
 	int res;
@@ -3640,13 +3649,18 @@ static int unregister_console_locked(str
 	for_each_console(c) {
 		if (c->flags & CON_BOOT)
 			found_boot_con = true;
-		if (!(c->flags & CON_NBCON))
+
+		if (c->flags & CON_NBCON)
+			found_nbcon_con = true;
+		else
 			found_legacy_con = true;
 	}
 	if (!found_boot_con)
 		have_boot_console = false;
 	if (!found_legacy_con)
 		have_legacy_console = false;
+	if (!found_nbcon_con)
+		have_nbcon_console = false;
 
 	return res;
 }
