From: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Date: Fri, 2 Feb 2018 21:13:00 -0800
Subject: drm/vblank: Do not update vblank count if interrupts are already
 disabled.
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Git-commit: 68036b08b91bc491ccc308f902616a570a49227c
Patch-mainline: v4.17-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

Updating vblank counts requires register reads and these reads may not
return meaningful values if the device was in a low power state after
vblank interrupts were last disabled. So, update the count only if vblank
interrupts are enabled. Secondly, this means the registers should be read
before disabling vblank interrupts.

v2: Don't check vblank->enabled outside it's lock (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Michel Dänzer <michel@daenzer.net>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180203051302.9974-8-dhinakaran.pandiyan@intel.com

Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/drm_vblank.c |   18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -353,23 +353,25 @@ void drm_vblank_disable_and_save(struct
 	spin_lock_irqsave(&dev->vblank_time_lock, irqflags);
 
 	/*
-	 * Only disable vblank interrupts if they're enabled. This avoids
-	 * calling the ->disable_vblank() operation in atomic context with the
-	 * hardware potentially runtime suspended.
+	 * Update vblank count and disable vblank interrupts only if the
+	 * interrupts were enabled. This avoids calling the ->disable_vblank()
+	 * operation in atomic context with the hardware potentially runtime
+	 * suspended.
 	 */
-	if (vblank->enabled) {
-		__disable_vblank(dev, pipe);
-		vblank->enabled = false;
-	}
+	if (!vblank->enabled)
+		goto out;
 
 	/*
-	 * Always update the count and timestamp to maintain the
+	 * Update the count and timestamp to maintain the
 	 * appearance that the counter has been ticking all along until
 	 * this time. This makes the count account for the entire time
 	 * between drm_crtc_vblank_on() and drm_crtc_vblank_off().
 	 */
 	drm_update_vblank_count(dev, pipe, false);
+	__disable_vblank(dev, pipe);
+	vblank->enabled = false;
 
+out:
 	spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags);
 }