[PATCH printk v2 20/26] printk: Track nbcon consoles

[John Ogness <john.ogness@linutronix.de>]

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>
---
 kernel/printk/printk.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 336dad179b99..2c4ab717c110 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -470,6 +470,13 @@ 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.
+ */
+static 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
@@ -3522,6 +3529,7 @@ void register_console(struct console *newcon)
 	console_init_seq(newcon, bootcon_registered);
 
 	if (newcon->flags & CON_NBCON) {
+		have_nbcon_console = true;
 		nbcon_init(newcon);
 	} else {
 		have_legacy_console = true;
@@ -3583,6 +3591,7 @@ 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;
@@ -3639,13 +3648,18 @@ static int unregister_console_locked(struct console *console)
 	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;
 }
-- 
2.39.2