[Intel-gfx] [PATCH] don't enable vblanks on disabled pipes

[Jesse Barnes]

In some cases we might try to wait on vblank events from pipes that aren't 
actually enabled.  We shouldn't allow this, so return -EINVAL if the pipe 
isn't on.

-- 
Jesse Barnes, Intel Open Source Technology Center

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 69b9a42..81ac2bd 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -400,6 +400,12 @@ int i915_enable_vblank(struct drm_device *dev, int pipe)
 {
 	drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 	unsigned long irqflags;
+	int pipeconf_reg = (pipe == 0) ? PIPEACONF : PIPEBCONF;
+	u32 pipeconf;
+
+	pipeconf = I915_READ(pipeconf_reg);
+	if (!(pipeconf & PIPEACONF_ENABLE))
+		return -EINVAL;
 
 	spin_lock_irqsave(&dev_priv->user_irq_lock, irqflags);
 	if (IS_I965G(dev))