drm: Stop using drm_vblank_count() as the hw frame counter

drm_vblank_count() returns the software counter. We should not pretend
it's the hw counter since we use the hw counter to figuere out what the
software counter value should be. So instead provide a new function
drm_vblank_no_hw_counter() for drivers that don't have a real hw
counter. The new function simply returns 0, which is about the only
thing it can do.

Cc: Vincent Abriou <vincent.abriou@st.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Vincent Abriou <vincent.abriou@st.com>
[danvet: s/int pipe/unsigned int pipe/ to follow Thierry's interface
change.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 1cb1e84..3dc56d34 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -953,6 +953,7 @@
 extern void drm_crtc_vblank_reset(struct drm_crtc *crtc);
 extern void drm_crtc_vblank_on(struct drm_crtc *crtc);
 extern void drm_vblank_cleanup(struct drm_device *dev);
+extern u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe);
 
 extern int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
 						 unsigned int pipe, int *max_error,