[PATCH v3 1/2] dummycon: Add dummycon_(un)register_switch_notifier

[Daniel van Vugt <daniel.van.vugt@xxxxxxxxxxxxx>]

To detect switch attempts before a real console exists. This will be
used for the same purpose as dummycon_(un)register_output_notifier,
for fbcon to detect a more polite time to take over.

Signed-off-by: Daniel van Vugt <daniel.van.vugt@xxxxxxxxxxxxx>
---
 drivers/video/console/dummycon.c | 35 +++++++++++++++++++++++++++-----
 include/linux/console.h          |  2 ++
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
index 14af5d9e13..55e9b600ce 100644
--- a/drivers/video/console/dummycon.c
+++ b/drivers/video/console/dummycon.c
@@ -83,6 +83,32 @@ static int dummycon_blank(struct vc_data *vc, int blank, int mode_switch)
 	/* Redraw, so that we get putc(s) for output done while blanked */
 	return 1;
 }
+
+/* This is protected by the console_lock */
+static RAW_NOTIFIER_HEAD(dummycon_switch_nh);
+
+void dummycon_register_switch_notifier(struct notifier_block *nb)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	raw_notifier_chain_register(&dummycon_switch_nh, nb);
+}
+
+void dummycon_unregister_switch_notifier(struct notifier_block *nb)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	raw_notifier_chain_unregister(&dummycon_switch_nh, nb);
+}
+
+static int dummycon_switch(struct vc_data *vc)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	raw_notifier_call_chain(&dummycon_switch_nh, 0, vc);
+
+	return 0;
+}
 #else
 static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos) { }
 static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
@@ -91,6 +117,10 @@ static int dummycon_blank(struct vc_data *vc, int blank, int mode_switch)
 {
 	return 0;
 }
+static int dummycon_switch(struct vc_data *vc)
+{
+	return 0;
+}
 #endif
 
 static const char *dummycon_startup(void)
@@ -120,11 +150,6 @@ static bool dummycon_scroll(struct vc_data *vc, unsigned int top,
 	return false;
 }
 
-static int dummycon_switch(struct vc_data *vc)
-{
-	return 0;
-}
-
 /*
  *  The console `switch' structure for the dummy console
  *
diff --git a/include/linux/console.h b/include/linux/console.h
index 779d388af8..8fd70ae623 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -531,5 +531,7 @@ extern void console_init(void);
 /* For deferred console takeover */
 void dummycon_register_output_notifier(struct notifier_block *nb);
 void dummycon_unregister_output_notifier(struct notifier_block *nb);
+void dummycon_register_switch_notifier(struct notifier_block *nb);
+void dummycon_unregister_switch_notifier(struct notifier_block *nb);
 
 #endif /* _LINUX_CONSOLE_H */
-- 
2.43.0