[PATCH 4.9 48/66] drm/i915: prevent crash with .disable_display parameter

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Clint Taylor <clinton.a.taylor@xxxxxxxxx>

commit 27892bbdc9233f33bf0f44e08aab8f12e0dec142 upstream.

The .disable_display parameter was causing a fatal crash when fbdev
was dereferenced during driver init.

V1: protection in i915_drv.c
V2: Moved protection to intel_fbdev.c

Fixes: 43cee314345a ("drm/i915/fbdev: Limit the global async-domain synchronization")
Testcase: igt/drv_module_reload/basic-no-display
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Clint Taylor <clinton.a.taylor@xxxxxxxxx>
Link: http://patchwork.freedesktop.org/patch/msgid/1484775523-29428-1-git-send-email-clinton.a.taylor@xxxxxxxxx
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Lukas Wunner <lukas@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
(cherry picked from commit 5b8cd0755f8a06a851c436a013e7be0823fb155a)
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/intel_fbdev.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -745,6 +745,9 @@ void intel_fbdev_initial_config_async(st
 {
 	struct intel_fbdev *ifbdev = to_i915(dev)->fbdev;
 
+	if (!ifbdev)
+		return;
+
 	ifbdev->cookie = async_schedule(intel_fbdev_initial_config, ifbdev);
 }