[PATCH v3 3/4] drm/vblank: estimate vblank while disabling vblank if interrupt disabled

[Robert Beckett <bob.beckett@collabora.com>]

If interrupts are disabled (e.g. via vblank_disable_fn) and we come to
disable vblank, update the vblank count to best guess as to what it
would be had the interrupts remained enabled, and update the timesamp to
now.

This avoids a stale vblank event being sent while disabling crtcs during
atomic modeset.

Fixes: 68036b08b91bc ("drm/vblank: Do not update vblank count if interrupts
are already disabled.")

Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
---
 drivers/gpu/drm/drm_vblank.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 7dabb2bdb733..db68b8cbf797 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -375,9 +375,23 @@ void drm_vblank_disable_and_save(struct drm_device *dev, unsigned int pipe)
 	 * interrupts were enabled. This avoids calling the ->disable_vblank()
 	 * operation in atomic context with the hardware potentially runtime
 	 * suspended.
+	 * If interrupts are disabled (e.g. via blank_disable_fn) then make
+	 * best guess as to what it would be now and make sure we have an up
+	 * to date timestamp.
 	 */
-	if (!vblank->enabled)
+	if (!vblank->enabled) {
+		ktime_t now = ktime_get();
+		u32 diff = 0;
+		if (vblank->framedur_ns) {
+			u64 diff_ns = ktime_to_ns(ktime_sub(now, vblank->time));
+			diff = DIV_ROUND_CLOSEST_ULL(diff_ns,
+						     vblank->framedur_ns);
+		}
+
+		store_vblank(dev, pipe, diff, now, vblank->count);
+
 		goto out;
+	}
 
 	/*
 	 * Update the count and timestamp to maintain the
-- 
2.18.0