drm/i915: Restore the KMS modeset for every activated CRTC

Restore the modeset for every activated CRTC in course of resume.
This is realized by calling the function of drm_helper_resume_force_mode.
Note: it is meaningful only for the KMS mode.

https://bugs.freedesktop.org/show_bug.cgi?id=21719
https://bugs.freedesktop.org/show_bug.cgi?id=21708
https://bugs.freedesktop.org/show_bug.cgi?id=22285
https://bugs.freedesktop.org/show_bug.cgi?id=22263

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_drv.c

@@ -35,6 +35,7 @@
 
 #include "drm_pciids.h"
 #include <linux/console.h>
+#include "drm_crtc_helper.h"
 
 static unsigned int i915_modeset = -1;
 module_param_named(modeset, i915_modeset, int, 0400);
@@ -115,6 +116,10 @@ static int i915_resume(struct drm_device *dev)
 
 		drm_irq_install(dev);
 	}
+	if (drm_core_check_feature(dev, DRIVER_MODESET)) {
+		/* Resume the modeset for every activated CRTC */
+		drm_helper_resume_force_mode(dev);
+	}
 
 	return ret;
 }