[Intel-gfx] [PATCH] Revert "drm/i915: Fix races on fbdev"

[Joonas Lahtinen]

This reverts commit a7442b93cf32c1e1ddb721a26cd1f92302e2a222.

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: a7442b93cf32 ("drm/i915: Fix races on fbdev")
Cc: Lukas Wunner <lukas at wunner.de>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tomi Sarvela <tomi.p.sarvela at intel.com>
Cc: stable at vger.kernel.org
Acked-by: Lukas Wunner <lukas at wunner.de>
Tested-by: Tomi Sarvela <tomi.p.sarvela at intel.com>
Suggested-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_dma.c    | 8 +++++---
 drivers/gpu/drm/i915/intel_fbdev.c | 3 ---
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index a66ce49..b377753 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/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);
 
diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index 4cf04ce..79ac202 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/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;
 
-- 
2.5.5