drm/i915: take mode config lock around crtc disable at suspend

This is just a theoretical issue, but we need to do this to prevent the
WARN in pipe_from_connector at suspend time.

This regression has been introduce in

commit 7bd688cd66db93f6430f6e2b3145ee5686daa315
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Fri Nov 8 16:48:56 2013 +0200

    drm/i915: handle backlight through chip specific functions

https://bugs.freedesktop.org/show_bug.cgi?id=71978
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 989be12cdd6e..2e367a1c6a64 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -534,8 +534,10 @@ static int i915_drm_freeze(struct drm_device *dev)
                  * Disable CRTCs directly since we want to preserve sw state
                  * for _thaw.
                  */
+                mutex_lock(&dev->mode_config.mutex);
                 list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
                         dev_priv->display.crtc_disable(crtc);
+                mutex_unlock(&dev->mode_config.mutex);
 
                 intel_modeset_suspend_hw(dev);
         }