Revert "drm/i915: Fix races on fbdev"

This reverts commit a7442b93.

With the patch applied SNB, IVB and ILK are experiencing hard machine
hangs. Original patch was to fix "just" kernel panics so it's not a good
trade-off.

Proper fix for the panic is on the way, lets revert until then.

Fixes: a7442b93 ("drm/i915: Fix races on fbdev")
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tomi Sarvela <tomi.p.sarvela@intel.com>
Cc: stable@vger.kernel.org
Acked-by: Lukas Wunner <lukas@wunner.de>
Tested-by: Tomi Sarvela <tomi.p.sarvela@intel.com>
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459510861-29035-1-git-send-email-joonas.lahtinen@linux.intel.com

drivers/gpu/drm/i915/i915_dma.c

@@ -493,9 +493,11 @@ static int i915_load_modeset_init(struct drm_device *dev)
 	 * Some ports require correctly set-up hpd registers for detection to
 	 * work properly (leading to ghost connected connector status), e.g. VGA
 	 * on gm45.  Hence we can only set up the initial fbdev config after hpd
-	 * irqs are fully enabled. We protect the fbdev initial config scanning
-	 * against hotplug events by waiting in intel_fbdev_output_poll_changed
-	 * until the asynchronous thread has finished.
+	 * irqs are fully enabled. Now we should scan for the initial config
+	 * only once hotplug handling is enabled, but due to screwed-up locking
+	 * around kms/fbdev init we can't protect the fdbev initial config
+	 * scanning against hotplug events. Hence do this first and ignore the
+	 * tiny window where we will loose hotplug notifactions.
 	 */
 	intel_fbdev_initial_config_async(dev);
 

drivers/gpu/drm/i915/intel_fbdev.c

@@ -810,8 +810,6 @@ void intel_fbdev_set_suspend(struct drm_device *dev, int state, bool synchronous
 void intel_fbdev_output_poll_changed(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	async_synchronize_full();
 	if (dev_priv->fbdev)
 		drm_fb_helper_hotplug_event(&dev_priv->fbdev->helper);
 }
@@ -823,7 +821,6 @@ void intel_fbdev_restore_mode(struct drm_device *dev)
 	struct intel_fbdev *ifbdev = dev_priv->fbdev;
 	struct drm_fb_helper *fb_helper;
 
-	async_synchronize_full();
 	if (!ifbdev)
 		return;