drm/tilcdc: Do not update the next frame buffer close to vertical blank

Do not update the next frame buffer close to vertical blank. This is
to avoid situation when the frame changes between writing of
LCDC_DMA_FB_BASE_ADDR_0_REG and LCDC_DMA_FB_CEILING_ADDR_0_REG.
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>
[Added description to the patch]
Signed-off-by: NJyri Sarha <jsarha@ti.com>

drivers/gpu/drm/tilcdc/tilcdc_crtc.c

@@ -21,6 +21,8 @@
 #include "tilcdc_drv.h"
 #include "tilcdc_regs.h"
 
+#define TILCDC_VBLANK_SAFETY_THRESHOLD_US 1000
+
 struct tilcdc_crtc {
 	struct drm_crtc base;
 
@@ -29,8 +31,12 @@ struct tilcdc_crtc {
 	int dpms;
 	wait_queue_head_t frame_done_wq;
 	bool frame_done;
+	spinlock_t irq_lock;
+
+	ktime_t last_vblank;
 
 	struct drm_framebuffer *curr_fb;
+	struct drm_framebuffer *next_fb;
 
 	/* for deferred fb unref's: */
 	struct drm_flip_work unref_work;
@@ -146,6 +152,8 @@ static int tilcdc_crtc_page_flip(struct drm_crtc *crtc,
 	struct drm_device *dev = crtc->dev;
 	int r;
 	unsigned long flags;
+	s64 tdiff;
+	ktime_t next_vblank;
 
 	r = tilcdc_verify_fb(crtc, fb);
 	if (r)
@@ -162,12 +170,21 @@ static int tilcdc_crtc_page_flip(struct drm_crtc *crtc,
 
 	pm_runtime_get_sync(dev->dev);
 
+	spin_lock_irqsave(&tilcdc_crtc->irq_lock, flags);
+
+	next_vblank = ktime_add_us(tilcdc_crtc->last_vblank,
+		1000000 / crtc->hwmode.vrefresh);
 
-	set_scanout(crtc, fb);
+	tdiff = ktime_to_us(ktime_sub(next_vblank, ktime_get()));
+
+	if (tdiff >= TILCDC_VBLANK_SAFETY_THRESHOLD_US)
+		set_scanout(crtc, fb);
+	else
+		tilcdc_crtc->next_fb = fb;
 
-	spin_lock_irqsave(&dev->event_lock, flags);
 	tilcdc_crtc->event = event;
-	spin_unlock_irqrestore(&dev->event_lock, flags);
+
+	spin_unlock_irqrestore(&tilcdc_crtc->irq_lock, flags);
 
 	pm_runtime_put_sync(dev->dev);
 
@@ -211,6 +228,12 @@ void tilcdc_crtc_dpms(struct drm_crtc *crtc, int mode)
 
 		pm_runtime_put_sync(dev->dev);
 
+		if (tilcdc_crtc->next_fb) {
+			drm_flip_work_queue(&tilcdc_crtc->unref_work,
+					    tilcdc_crtc->next_fb);
+			tilcdc_crtc->next_fb = NULL;
+		}
+
 		if (tilcdc_crtc->curr_fb) {
 			drm_flip_work_queue(&tilcdc_crtc->unref_work,
 					    tilcdc_crtc->curr_fb);
@@ -651,19 +674,39 @@ irqreturn_t tilcdc_crtc_irq(struct drm_crtc *crtc)
 
 	if (stat & LCDC_END_OF_FRAME0) {
 		unsigned long flags;
+		bool skip_event = false;
+		ktime_t now;
+
+		now = ktime_get();
 
 		drm_flip_work_commit(&tilcdc_crtc->unref_work, priv->wq);
 
+		spin_lock_irqsave(&tilcdc_crtc->irq_lock, flags);
+
+		tilcdc_crtc->last_vblank = now;
+
+		if (tilcdc_crtc->next_fb) {
+			set_scanout(crtc, tilcdc_crtc->next_fb);
+			tilcdc_crtc->next_fb = NULL;
+			skip_event = true;
+		}
+
+		spin_unlock_irqrestore(&tilcdc_crtc->irq_lock, flags);
+
 		drm_handle_vblank(dev, 0);
 
-		spin_lock_irqsave(&dev->event_lock, flags);
+		if (!skip_event) {
+			struct drm_pending_vblank_event *event;
 
-		if (tilcdc_crtc->event) {
-			drm_send_vblank_event(dev, 0, tilcdc_crtc->event);
+			spin_lock_irqsave(&dev->event_lock, flags);
+
+			event = tilcdc_crtc->event;
 			tilcdc_crtc->event = NULL;
-		}
+			if (event)
+				drm_send_vblank_event(dev, 0, event);
 
-		spin_unlock_irqrestore(&dev->event_lock, flags);
+			spin_unlock_irqrestore(&dev->event_lock, flags);
+		}
 	}
 
 	if (priv->rev == 2) {
@@ -697,6 +740,8 @@ struct drm_crtc *tilcdc_crtc_create(struct drm_device *dev)
 	drm_flip_work_init(&tilcdc_crtc->unref_work,
 			"unref", unref_worker);
 
+	spin_lock_init(&tilcdc_crtc->irq_lock);
+
 	ret = drm_crtc_init(dev, crtc, &tilcdc_crtc_funcs);
 	if (ret < 0)
 		goto fail;