[PATCH 5/7] drm/vblank: timer: Estimate vblank timeout if timer is disabled

[Thomas Zimmermann <tzimmermann@suse.de>]

Estimate the next vblank timeout from the duration of a frame in
the currently programmed display mode. Timeouts are aligned to
frame duration, so we can round up to the next alignment.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/drm_vblank.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index cecaef98aa52..b5d2fb741b2d 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -2333,6 +2333,17 @@ bool drm_crtc_vblank_get_vblank_timeout(struct drm_crtc *crtc, ktime_t *vblank_t
 			return false; /* already expired */
 
 		framedur_ns = vblank->framedur_ns;
+	} else if (mode->crtc_clock) {
+		u64 framesize = mode->crtc_htotal * mode->crtc_vtotal;
+
+		/*
+		 * With the vblank timer being disabled, we don't have an
+		 * expiry time. As the timeouts are aligned to the display
+		 * mode's clock, we can estimate when the expiry time would
+		 * have been.
+		 */
+		framedur_ns = div_u64(framesize * 1000000llu, mode->crtc_clock);
+		*vblank_time = roundup(ktime_get_ns(), framedur_ns);
 	} else {
 		return false;
 	}
-- 
2.54.0