drm/atomic: Handle 64-bit return from drm_crtc_vblank_count()

570e8696 ("drm: Widen vblank count to 64-bits [v3]") changed the
return type for drm_crtc_vblank_count() to u64.

The flip ioctl receives a 32-bit target sequence from user space and is
compared against the current sequence from drm_crtc_vblank_count(). So,
typecast return from drm_crtc_vblank_count() explicitly to add clarity.

__drm_crtcs_state.last_vblank_count however only ever stores the value from
drm_crtc_vblank_count() and can be upgraded to u64.

Cc: Keith Packard <keithp@keithp.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180203051302.9974-7-dhinakaran.pandiyan@intel.com

drivers/gpu/drm/drm_plane.c

@@ -944,7 +944,7 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 		if (r)
 			return r;
 
-		current_vblank = drm_crtc_vblank_count(crtc);
+		current_vblank = (u32)drm_crtc_vblank_count(crtc);
 
 		switch (page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET) {
 		case DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE:

include/drm/drm_atomic.h

@@ -145,7 +145,7 @@ struct __drm_crtcs_state {
 	struct drm_crtc *ptr;
 	struct drm_crtc_state *state, *old_state, *new_state;
 	s32 __user *out_fence_ptr;
-	unsigned last_vblank_count;
+	u64 last_vblank_count;
 };
 
 struct __drm_connnectors_state {