drm/panic: Add a kmsg panic screen

Add a kmsg option, which will display the last lines of kmsg,
and should be similar to fbcon.
Add a drm.panic_screen module parameter, so you can choose between
the different panic screens available.
two options currently, but more will be added later:
 * "user": a short message telling the user to reboot the machine.
 * "kmsg": fill the screen with the last lines of kmsg.

You can even change it at runtime by writing to
/sys/module/drm/parameters/panic_screen

v2:
 * Use module parameter instead of Kconfig choice
   (Javier Martinez Canillas)

v3:
 * Add help for module parameter usage in Kconfig
   (Javier Martivez Canillas)
 * Fix use of font->height before checking it isn't null.
   (kernel test robot, Dan Carpenter)

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240603095343.39588-4-jfalempe@redhat.com

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 9703429de6b9..a9df94291622 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -137,6 +137,19 @@ config DRM_PANIC_DEBUG
 	  This is unsafe and should not be enabled on a production build.
 	  If in doubt, say "N".
 
+config DRM_PANIC_SCREEN
+	string "Panic screen formater"
+	default "user"
+	depends on DRM_PANIC
+	help
+	  This option enable to choose what will be displayed when a kernel
+	  panic occurs. You can choose between "user", a short message telling
+	  the user to reboot the system, or "kmsg" which will display the last
+	  lines of kmsg.
+	  This can also be overridden by drm.panic_screen=xxxx kernel parameter
+	  or by writing to /sys/module/drm/parameters/panic_screen sysfs entry
+	  Default is "user"
+
 config DRM_DEBUG_DP_MST_TOPOLOGY_REFS
         bool "Enable refcount backtrace history in the DP MST helpers"
 	depends on STACKTRACE_SUPPORT