drm/i915: Can't do accurate vblank timestamps with UMS

Disable this feature when KMS is not running by setting the
driver->get_vblank_timestamp function pointer to NULL.

Signed-off-by: Keith Packard <keithp@keithp.com>
Tested-by: Justin P. Mattock <justinmattock@gmail.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 02f96fd0d52d..9cbb0cd8f46a 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2058,8 +2058,10 @@ void intel_irq_init(struct drm_device *dev)
                 dev->driver->get_vblank_counter = gm45_get_vblank_counter;
         }
 
-
-        dev->driver->get_vblank_timestamp = i915_get_vblank_timestamp;
+        if (drm_core_check_feature(dev, DRIVER_MODESET))
+                dev->driver->get_vblank_timestamp = i915_get_vblank_timestamp;
+        else
+                dev->driver->get_vblank_timestamp = NULL;
         dev->driver->get_scanout_position = i915_get_crtc_scanoutpos;
 
         if (IS_IVYBRIDGE(dev)) {