[PATCH v8 3/8] drm/panic: Add debugfs entry to test without triggering panic.

[Jocelyn Falempe]

Add a debugfs file, so you can test drm_panic without freezing
your machine. This is unsafe, and should be enabled only for
developer or tester.

to display the drm_panic screen, just run:
echo 1 > /sys/kernel/debug/drm_panic/trigger

Signed-off-by: Jocelyn Falempe <jfalempe at redhat.com>
---
 drivers/gpu/drm/Kconfig     |  9 +++++++
 drivers/gpu/drm/drm_panic.c | 47 +++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index c17d8a8f6877..8dcea29f595c 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -125,6 +125,15 @@ config DRM_PANIC_BACKGROUND_COLOR
 	depends on DRM_PANIC
 	default 0x000000
 
+config DRM_PANIC_DEBUG
+	bool "Add a debug fs entry to trigger drm_panic"
+	depends on DRM_PANIC && DEBUG_FS
+	help
+	  Add drm_panic/trigger in the kernel debugfs, to force the panic
+	  handler to write the panic message to the scanout buffer. This is
+	  unsafe and should not be enabled on a production build.
+	  If in doubt, say "N".
+
 config DRM_DEBUG_DP_MST_TOPOLOGY_REFS
         bool "Enable refcount backtrace history in the DP MST helpers"
 	depends on STACKTRACE_SUPPORT
diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
index c9f386476ef9..c5d3f725c5f5 100644
--- a/drivers/gpu/drm/drm_panic.c
+++ b/drivers/gpu/drm/drm_panic.c
@@ -398,3 +398,50 @@ void drm_panic_unregister(struct drm_plane *plane)
 }
 EXPORT_SYMBOL(drm_panic_unregister);
 
+
+/*
+ * DEBUG, This is currently unsafe.
+ * Also it will call all panic_notifier, since there is no way to filter and
+ * only call the drm_panic notifier.
+ */
+#ifdef CONFIG_DRM_PANIC_DEBUG
+#include <linux/debugfs.h>
+
+static struct dentry *debug_dir;
+static struct dentry *debug_trigger;
+
+static ssize_t dbgfs_trigger_write(struct file *file, const char __user *user_buf,
+				   size_t count, loff_t *ppos)
+{
+	bool run;
+
+	if (kstrtobool_from_user(user_buf, count, &run) == 0 && run)
+		atomic_notifier_call_chain(&panic_notifier_list, 0, "Test drm panic from debugfs");
+	return count;
+}
+
+static const struct file_operations dbg_drm_panic_ops = {
+	.owner = THIS_MODULE,
+	.write = dbgfs_trigger_write,
+};
+
+static int __init debugfs_start(void)
+{
+	debug_dir = debugfs_create_dir("drm_panic", NULL);
+
+	if (IS_ERR(debug_dir))
+		return PTR_ERR(debug_dir);
+	debug_trigger = debugfs_create_file("trigger", 0200, debug_dir,
+					    NULL, &dbg_drm_panic_ops);
+	return 0;
+}
+
+static void __exit debugfs_end(void)
+{
+	debugfs_remove_recursive(debug_dir);
+}
+
+module_init(debugfs_start);
+module_exit(debugfs_end);
+
+#endif
-- 
2.43.0