[PATCH] drm/i915/display: Make intel_crtc_get_vblank_counter safe on PREEMPT_RT

[Maarten Lankhorst]

drm_crtc_accurate_vblank_count takes a spinlock, which we should avoid
in tracepoints and debug functions.

This also prevents taking the spinlock 2x during the critical
section of pipe updates for DSI updates.

Signed-off-by: Maarten Lankhorst <d...@lankhorst.se>
---
 drivers/gpu/drm/i915/display/intel_crtc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c 
b/drivers/gpu/drm/i915/display/intel_crtc.c
index a187db6df2d36..cee00aa2c79de 100644
--- a/drivers/gpu/drm/i915/display/intel_crtc.c
+++ b/drivers/gpu/drm/i915/display/intel_crtc.c
@@ -84,8 +84,12 @@ u32 intel_crtc_get_vblank_counter(struct intel_crtc *crtc)
        if (!crtc->active)
                return 0;
 
-       if (!vblank->max_vblank_count)
-               return (u32)drm_crtc_accurate_vblank_count(&crtc->base);
+       if (!vblank->max_vblank_count) {
+               if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+                       return (u32)drm_crtc_accurate_vblank_count(&crtc->base);
+               else
+                       return (u32)drm_crtc_vblank_count(&crtc->base);
+       }
 
        return crtc->base.funcs->get_vblank_counter(&crtc->base);
 }
-- 
2.50.0