drm: Populate fb->dev from drm_helper_mode_fill_fb_struct()

Populating fb->dev before drm_framebuffer_init() allows us to use
fb->dev already while validating the framebuffer. Let's have
drm_helper_mode_fill_fb_struct() do that for us.

Also make drm_framebuffer_init() warn us if a different device
pointer is passed to it than was passed to
drm_helper_mode_fill_fb_struct().

v2: Reject fbs with invalid fb->dev (Laurent)

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com> (v1)
Link: http://patchwork.freedesktop.org/patch/msgid/1479498793-31021-19-git-send-email-ville.syrjala@linux.intel.com

drivers/gpu/drm/drm_framebuffer.c

@@ -631,8 +631,11 @@ int drm_framebuffer_init(struct drm_device *dev, struct drm_framebuffer *fb,
 {
 	int ret;
 
+	if (WARN_ON_ONCE(fb->dev != dev))
+		return -EINVAL;
+
 	INIT_LIST_HEAD(&fb->filp_head);
-	fb->dev = dev;
+
 	fb->funcs = funcs;
 
 	ret = drm_mode_object_get_reg(dev, &fb->base, DRM_MODE_OBJECT_FB,

drivers/gpu/drm/drm_modeset_helper.c

@@ -90,6 +90,7 @@ void drm_helper_mode_fill_fb_struct(struct drm_device *dev,
 		fb->bits_per_pixel = info->cpp[0] * 8;
 	}
 
+	fb->dev = dev;
 	fb->width = mode_cmd->width;
 	fb->height = mode_cmd->height;
 	for (i = 0; i < 4; i++) {