[PATCH v2 5/8] drm/vblank: Restoring vblank counts after device runtime PM events.

[Dhinakaran Pandiyan]

The HW frame counter can get reset when devices enters low power
states and this messes up any following vblank count updates. So, compute
the missed vblank interrupts for that low power state duration using time
stamps. This is similar to _crtc_vblank_on() except that it doesn't enable
vblank interrupts because this function is expected to be called from
the driver _enable_vblank() vfunc.

Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
---
 drivers/gpu/drm/drm_vblank.c | 33 +++++++++++++++++++++++++++++++++
 include/drm/drm_vblank.h     |  1 +
 2 files changed, 34 insertions(+)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 7eee82c06ed8..494e2cff6e55 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1230,6 +1230,39 @@ void drm_crtc_vblank_on(struct drm_crtc *crtc)
 }
 EXPORT_SYMBOL(drm_crtc_vblank_on);
 
+void drm_crtc_vblank_restore(struct drm_device *dev, unsigned int pipe)
+{
+	ktime_t t_vblank;
+	struct drm_vblank_crtc *vblank;
+	int framedur_ns;
+	u64 diff_ns;
+	u32 cur_vblank, diff = 1;
+	int count = DRM_TIMESTAMP_MAXRETRIES;
+
+	if (WARN_ON(pipe >= dev->num_crtcs))
+		return;
+
+	vblank = &dev->vblank[pipe];
+	WARN_ONCE((drm_debug & DRM_UT_VBL) && !vblank->framedur_ns,
+		  "Cannot compute missed vblanks without frame duration\n");
+	framedur_ns = vblank->framedur_ns;
+
+	do {
+		cur_vblank = __get_vblank_counter(dev, pipe);
+		drm_get_last_vbltimestamp(dev, pipe, &t_vblank, false);
+	} while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
+
+	diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
+	if (framedur_ns)
+		diff = DIV_ROUND_CLOSEST_ULL(diff_ns, framedur_ns);
+
+
+	DRM_DEBUG_VBL("missed %d vblanks in %lld ns, frame duration=%d ns, hw_diff=%d\n",
+		      diff, diff_ns, framedur_ns, cur_vblank - vblank->last);
+	store_vblank(dev, pipe, diff, t_vblank, cur_vblank);
+}
+EXPORT_SYMBOL(drm_crtc_vblank_restore);
+
 static void drm_legacy_vblank_pre_modeset(struct drm_device *dev,
 					  unsigned int pipe)
 {
diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index 848b463a0af5..aafcbef91bd7 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -180,6 +180,7 @@ void drm_crtc_vblank_off(struct drm_crtc *crtc);
 void drm_crtc_vblank_reset(struct drm_crtc *crtc);
 void drm_crtc_vblank_on(struct drm_crtc *crtc);
 u32 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc);
+void drm_crtc_vblank_restore(struct drm_device *dev, unsigned int pipe);
 
 bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
 					   unsigned int pipe, int *max_error,
-- 
2.11.0