The ->lastclose callback invokes intel_fbdev_restore_mode() and has
been witnessed to run before intel_fbdev_initial_config_async()
has finished.

We might likewise receive hotplug events or be suspended before
we've had a chance to fully set up the fbdev.

Fix by waiting for the asynchronous thread to finish.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93580
Reported-by: Gustav Fägerlind <gustav.fagerl...@gmail.com>
Reported-by: "Li, Weinan Z" <weinan.z...@intel.com>
Cc: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: sta...@vger.kernel.org
Signed-off-by: Lukas Wunner <lu...@wunner.de>
---
 drivers/gpu/drm/i915/i915_dma.c    | 8 +++-----
 drivers/gpu/drm/i915/intel_fbdev.c | 4 ++++
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index a0f5659..a76b528 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -437,11 +437,9 @@ 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. 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.
+        * 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.
         */
        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 09840f4..2002b13 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -749,6 +749,7 @@ void intel_fbdev_set_suspend(struct drm_device *dev, int 
state, bool synchronous
        struct intel_fbdev *ifbdev = dev_priv->fbdev;
        struct fb_info *info;
 
+       async_synchronize_full();
        if (!ifbdev)
                return;
 
@@ -795,6 +796,8 @@ 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);
 }
@@ -806,6 +809,7 @@ 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;
 
-- 
1.8.5.2 (Apple Git-48)

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