1 files changed, 42 insertions, 3 deletions

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 98e091175921..cde71ee95a8f 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
         write_sequnlock(&vblank->seqlock);
 }
 
+static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
+{
+        struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+
+        return vblank->max_vblank_count ?: dev->max_vblank_count;
+}
+
 /*
  * "No hw counter" fallback implementation of .get_vblank_counter() hook,
  * if there is no useable hardware frame counter available.
  */
 static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
 {
-        WARN_ON_ONCE(dev->max_vblank_count != 0);
+        WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
         return 0;
 }
 
@@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
         ktime_t t_vblank;
         int count = DRM_TIMESTAMP_MAXRETRIES;
         int framedur_ns = vblank->framedur_ns;
+        u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
 
         /*
          * Interrupts were disabled prior to this call, so deal with counter
@@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
                 rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
         } while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
 
-        if (dev->max_vblank_count != 0) {
+        if (max_vblank_count) {
                 /* trust the hw counter when it's around */
-                diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
+                diff = (cur_vblank - vblank->last) & max_vblank_count;
         } else if (rc && framedur_ns) {
                 u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
 
@@ -1205,6 +1213,37 @@ void drm_crtc_vblank_reset(struct drm_crtc *crtc)
 EXPORT_SYMBOL(drm_crtc_vblank_reset);
 
 /**
+ * drm_crtc_set_max_vblank_count - configure the hw max vblank counter value
+ * @crtc: CRTC in question
+ * @max_vblank_count: max hardware vblank counter value
+ *
+ * Update the maximum hardware vblank counter value for @crtc
+ * at runtime. Useful for hardware where the operation of the
+ * hardware vblank counter depends on the currently active
+ * display configuration.
+ *
+ * For example, if the hardware vblank counter does not work
+ * when a specific connector is active the maximum can be set
+ * to zero. And when that specific connector isn't active the
+ * maximum can again be set to the appropriate non-zero value.
+ *
+ * If used, must be called before drm_vblank_on().
+ */
+void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
+                                   u32 max_vblank_count)
+{
+        struct drm_device *dev = crtc->dev;
+        unsigned int pipe = drm_crtc_index(crtc);
+        struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+
+        WARN_ON(dev->max_vblank_count);
+        WARN_ON(!READ_ONCE(vblank->inmodeset));
+
+        vblank->max_vblank_count = max_vblank_count;
+}
+EXPORT_SYMBOL(drm_crtc_set_max_vblank_count);
+
+/**
  * drm_crtc_vblank_on - enable vblank events on a CRTC
  * @crtc: CRTC in question
  *