Patch "dummycon: Trigger redraw when switching consoles with deferred takeover" has been added to the 6.12-stable tree

[gregkh at linuxfoundation.org]

This is a note to let you know that I've just added the patch titled

    dummycon: Trigger redraw when switching consoles with deferred takeover

to the 6.12-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     dummycon-trigger-redraw-when-switching-consoles-with-deferred-takeover.patch
and it can be found in the queue-6.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.


>From 03bcbbb3995ba5df43af9aba45334e35f2dfe27b Mon Sep 17 00:00:00 2001
From: Thomas Zimmermann <tzimmermann at suse.de>
Date: Tue, 20 May 2025 09:14:00 +0200
Subject: dummycon: Trigger redraw when switching consoles with deferred takeover

From: Thomas Zimmermann <tzimmermann at suse.de>

commit 03bcbbb3995ba5df43af9aba45334e35f2dfe27b upstream.

Signal vt subsystem to redraw console when switching to dummycon
with deferred takeover enabled. Makes the console switch to fbcon
and displays the available output.

With deferred takeover enabled, dummycon acts as the placeholder
until the first output to the console happens. At that point, fbcon
takes over. If the output happens while dummycon is not active, it
cannot inform fbcon. This is the case if the vt subsystem runs in
graphics mode.

A typical graphical boot starts plymouth, a display manager and a
compositor; all while leaving out dummycon. Switching to a text-mode
console leaves the console with dummycon even if a getty terminal
has been started.

Returning true from dummycon's con_switch helper signals the vt
subsystem to redraw the screen. If there's output available dummycon's
con_putc{s} helpers trigger deferred takeover of fbcon, which sets a
display mode and displays the output. If no output is available,
dummycon remains active.

v2:
- make the comment slightly more verbose (Javier)

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Reported-by: Andrei Borzenkov <arvidjaar at gmail.com>
Closes: https://bugzilla.suse.com/show_bug.cgi?id=1242191
Tested-by: Andrei Borzenkov <arvidjaar at gmail.com>
Acked-by: Javier Martinez Canillas <javierm at redhat.com>
Fixes: 83d83bebf401 ("console/fbcon: Add support for deferred console takeover")
Cc: Hans de Goede <hdegoede at redhat.com>
Cc: linux-fbdev at vger.kernel.org
Cc: dri-devel at lists.freedesktop.org
Cc: <stable at vger.kernel.org> # v4.19+
Link: https://lore.kernel.org/r/20250520071418.8462-1-tzimmermann@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 drivers/video/console/dummycon.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

--- a/drivers/video/console/dummycon.c
+++ b/drivers/video/console/dummycon.c
@@ -85,6 +85,15 @@ static bool dummycon_blank(struct vc_dat
 	/* Redraw, so that we get putc(s) for output done while blanked */
 	return true;
 }
+
+static bool dummycon_switch(struct vc_data *vc)
+{
+	/*
+	 * Redraw, so that we get putc(s) for output done while switched
+	 * away. Informs deferred consoles to take over the display.
+	 */
+	return true;
+}
 #else
 static void dummycon_putc(struct vc_data *vc, u16 c, unsigned int y,
 			  unsigned int x) { }
@@ -95,6 +104,10 @@ static bool dummycon_blank(struct vc_dat
 {
 	return false;
 }
+static bool dummycon_switch(struct vc_data *vc)
+{
+	return false;
+}
 #endif
 
 static const char *dummycon_startup(void)
@@ -123,11 +136,6 @@ static bool dummycon_scroll(struct vc_da
 {
 	return false;
 }
-
-static bool dummycon_switch(struct vc_data *vc)
-{
-	return false;
-}
 
 /*
  *  The console `switch' structure for the dummy console


Patches currently in stable-queue which might be from tzimmermann at suse.de are

queue-6.12/dummycon-trigger-redraw-when-switching-consoles-with-deferred-takeover.patch
queue-6.12/video-screen_info-relocate-framebuffers-behind-pci-bridges.patch
queue-6.12/sysfb-fix-screen_info-type-check-for-vga.patch