From: John Ogness <john.ogness@linutronix.de>
Date: Fri, 8 Dec 2023 15:54:27 +0000
Subject: [PATCH 104/134] printk: nbcon: Add driver_enter/driver_exit console
 callbacks
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz

Console drivers need some mechanism to synchronize between "normal
driver activity" and console printing. For uart serial drivers it
is the port lock. Other types of console drivers (network,
graphics, USB) will need something as well.

Provide 2 new mandatory nbcon console callbacks (driver_enter and
driver_exit) to allow the consoles drivers to implement the
appropriate synchronization. The callbacks are also expected to
disable/enable migration.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/console.h |    4 ++++
 1 file changed, 4 insertions(+)

--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -296,6 +296,8 @@ struct nbcon_write_context {
  * @node:		hlist node for the console list
  *
  * @write_atomic:	Write callback for atomic context
+ * @driver_enter:	Callback to begin synchronization with driver code
+ * @driver_exit:	Callback to finish synchronization with driver code
  * @nbcon_state:	State for nbcon consoles
  * @nbcon_seq:		Sequence number of the next record for nbcon to print
  * @pbufs:		Pointer to nbcon private buffer
@@ -323,6 +325,8 @@ struct console {
 	/* nbcon console specific members */
 	bool			(*write_atomic)(struct console *con,
 						struct nbcon_write_context *wctxt);
+	void			(*driver_enter)(struct console *con, unsigned long *flags);
+	void			(*driver_exit)(struct console *con, unsigned long flags);
 	atomic_t		__private nbcon_state;
 	atomic_long_t		__private nbcon_seq;
 	struct printk_buffers	*pbufs;
