[PATCH v2] drm/core: Add drm_accurate_vblank_count_and_time, v2.

[Maarten Lankhorst]

This function is useful for gen2 intel devices which have no frame
counter, but need a way to determine the current vblank count without
racing with the vblank interrupt handler.

intel_pipe_update_start checks if no vblank interrupt will occur
during vblank evasion, but cannot check whether the vblank handler has
run to completion. This function uses the timestamps to determine
when the last vblank has happened, and interpolates from there.

Changes since v1:
- Take vblank_time_lock and don't use drm_vblank_count_and_time.

Cc: Mario Kleiner <mario.kleiner.de at gmail.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
---
 drivers/gpu/drm/drm_irq.c | 31 +++++++++++++++++++++++++++++++
 include/drm/drmP.h        |  2 ++
 2 files changed, 33 insertions(+)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 3c1a6f18e71c..d3cecc1932e1 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -303,6 +303,37 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
 	store_vblank(dev, pipe, diff, &t_vblank, cur_vblank);
 }
 
+/**
+ * drm_accurate_vblank_count_and_time - retrieve the master vblank counter
+ * @crtc: which counter to retrieve
+ * @tv_ret: last time counter was updated
+ *
+ * This function is similar to @drm_update_vblank_count_and_time but
+ * this function interpolates to handle a race with vblank irq's, and
+ * is only useful for crtc's that have no hw vblank counter.
+ */
+
+u32 drm_accurate_vblank_count_and_time(struct drm_crtc *crtc,
+				       struct timeval *tv_ret)
+{
+	struct drm_device *dev = crtc->dev;
+	u32 vblank, pipe = drm_crtc_index(crtc);
+	unsigned long flags;
+
+	WARN(dev->max_vblank_count, "This function is only useful when a hw counter is unavailable.");
+
+	spin_lock_irqsave(&dev->vblank_time_lock, flags);
+	drm_update_vblank_count(dev, pipe, 0);
+
+	vblank = dev->vblank[pipe].count;
+	*tv_ret = vblanktimestamp(dev, pipe, vblank);
+
+	spin_unlock_irqrestore(&dev->vblank_time_lock, flags);
+
+	return vblank;
+}
+EXPORT_SYMBOL(drm_accurate_vblank_count_and_time);
+
 /*
  * Disable vblank irq's on crtc, make sure that last vblank count
  * of hardware and corresponding consistent software vblank counter
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 31483c2fef51..1df65922c7c6 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -995,6 +995,8 @@ extern void drm_crtc_vblank_off(struct drm_crtc *crtc);
 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_accurate_vblank_count_and_time(struct drm_crtc *crtc,
+					      struct timeval *tv_ret);
 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,
-- 
2.1.0