drm/amd/display: Add debugfs entry for amdgpu_dm_visual_confirm

[Why]
DC provides a few visual confirmation debug options that can be
dynamically changed at runtime to help debug surface programming issues
but we don't have any way to access it from userspace.

[How]
Add the amdgpu_dm_visual_confirm debugfs entry.
It accepts a string containing the DC visual confirm enum value using
the debugfs attribute helpers.

The debugfs_create_file_unsafe can be used instead of
debugfs_create_file as per the documentation.

v2: Use debugfs helpers for getting and setting the value (Christian)

Cc: Leo Li <sunpeng.li@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c

@@ -995,6 +995,35 @@ static const struct drm_info_list amdgpu_dm_debugfs_list[] = {
 	{"amdgpu_target_backlight_pwm", &target_backlight_read},
 };
 
+/*
+ * Sets the DC visual confirm debug option from the given string.
+ * Example usage: echo 1 > /sys/kernel/debug/dri/0/amdgpu_visual_confirm
+ */
+static int visual_confirm_set(void *data, u64 val)
+{
+	struct amdgpu_device *adev = data;
+
+	adev->dm.dc->debug.visual_confirm = (enum visual_confirm)val;
+
+	return 0;
+}
+
+/*
+ * Reads the DC visual confirm debug option value into the given buffer.
+ * Example usage: cat /sys/kernel/debug/dri/0/amdgpu_dm_visual_confirm
+ */
+static int visual_confirm_get(void *data, u64 *val)
+{
+	struct amdgpu_device *adev = data;
+
+	*val = adev->dm.dc->debug.visual_confirm;
+
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(visual_confirm_fops, visual_confirm_get,
+			 visual_confirm_set, "%llu\n");
+
 int dtn_debugfs_init(struct amdgpu_device *adev)
 {
 	static const struct file_operations dtn_log_fops = {
@@ -1020,5 +1049,13 @@ int dtn_debugfs_init(struct amdgpu_device *adev)
 		adev,
 		&dtn_log_fops);
 
-	return PTR_ERR_OR_ZERO(ent);
+	if (IS_ERR(ent))
+		return PTR_ERR(ent);
+
+	ent = debugfs_create_file_unsafe("amdgpu_dm_visual_confirm", 0644, root,
+					 adev, &visual_confirm_fops);
+	if (IS_ERR(ent))
+		return PTR_ERR(ent);
+
+	return 0;
 }