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.

v2:
        * don't hold helper->lock while waiting for vblank

Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>
---
 drivers/gpu/drm/drm_fb_helper.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index a7ba5b4902d6..d0cb1fa4f909 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -402,8 +402,18 @@ 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 */
+       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);
+       }
 
        spin_lock_irqsave(&helper->dirty_lock, flags);
        clip_copy = *clip;
-- 
2.23.0

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