From: John Ogness <john.ogness@linutronix.de>
Date: Wed, 22 Nov 2023 11:23:43 +0000
Subject: [PATCH 099/134] printk: Consider nbcon boot consoles on seq init
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz

If a non-boot console is registering and boot consoles exist, the
consoles are flushed before being unregistered. This allows the
non-boot console to continue where the boot console left off.

If for whatever reason flushing fails, the lowest seq found from
any of the enabled boot consoles is used. Until now con->seq was
checked. However, if it is an nbcon boot console, the function
nbcon_seq_read() must be used to read seq because con->seq is
always 0.

Check if it is an nbcon boot console and if so call
nbcon_seq_read() to read seq.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/printk/printk.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3392,11 +3392,20 @@ static void console_init_seq(struct cons
 
 				newcon->seq = prb_next_seq(prb);
 				for_each_console(con) {
-					if ((con->flags & CON_BOOT) &&
-					    (con->flags & CON_ENABLED) &&
-					    con->seq < newcon->seq) {
-						newcon->seq = con->seq;
+					u64 seq;
+
+					if (!((con->flags & CON_BOOT) &&
+					      (con->flags & CON_ENABLED))) {
+						continue;
 					}
+
+					if (con->flags & CON_NBCON)
+						seq = nbcon_seq_read(con);
+					else
+						seq = con->seq;
+
+					if (seq < newcon->seq)
+						newcon->seq = seq;
 				}
 			}
 
