[PATCH 1/2] drm/fb-helper: Synchronize dirty worker with vblank

[Thomas Zimmermann]

Before updating the display from the console's shadow buffer, the dirty
worker now waits for vblank. This allows several screen updates to pile
up and acts as a rate limiter.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
---
 drivers/gpu/drm/drm_fb_helper.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index a7ba5b4902d6..017e2f6bd1b9 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -402,8 +402,20 @@ static void drm_fb_helper_dirty_work(struct work_struct *work)
 						    dirty_work);
 	struct drm_clip_rect *clip = &helper->dirty_clip;
 	struct drm_clip_rect clip_copy;
+	struct drm_crtc *crtc;
 	unsigned long flags;
 	void *vaddr;
+	int ret;
+
+	/* rate-limit update frequency */
+	mutex_lock(&helper->lock);
+	crtc = helper->client.modesets[0].crtc;
+	ret = drm_crtc_vblank_get(crtc);
+	if (!ret) {
+		drm_crtc_wait_one_vblank(crtc);
+		drm_crtc_vblank_put(crtc);
+	}
+	mutex_unlock(&helper->lock);
 
 	spin_lock_irqsave(&helper->dirty_lock, flags);
 	clip_copy = *clip;
-- 
2.23.0