drm/i915: prevent crash with .disable_display parameter

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@chris-wilson.co.uk>
Signed-off-by: Clint Taylor <clinton.a.taylor@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1484775523-29428-1-git-send-email-clinton.a.taylor@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: <stable@vger.kernel.org> # v4.8+
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
(cherry picked from commit 5b8cd0755f8a06a851c436a013e7be0823fb155a)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index beb08982dc0b5c3ea9711de7220c383e6ea41b92..8cf2d80f22540a35dc4245a842d8473ce7d852d9 100644 (file)
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -742,6 +742,9 @@ void intel_fbdev_initial_config_async(struct drm_device *dev)
 {
        struct intel_fbdev *ifbdev = to_i915(dev)->fbdev;
 
+       if (!ifbdev)
+               return;
+
        ifbdev->cookie = async_schedule(intel_fbdev_initial_config, ifbdev);
 }