drm/i915: Restore the display config after a GPU reset on gen4

On pre-ctg GPU reset also resets the display hardware. Force a mode
restore after the GPU reset, and also re-init clock gating.

v2: Use intel_modeset_init_hw() instead of intel_init_clock_gating()
    in case more relevant stuff gets added there at some point
    Restore interrupts after the reset as well
Tested-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.c

@@ -880,6 +880,24 @@ int i915_reset(struct drm_device *dev)
 		 */
 		if (INTEL_INFO(dev)->gen > 5)
 			intel_reset_gt_powersave(dev);
+
+		if (IS_GEN4(dev) && !IS_G4X(dev)) {
+			intel_runtime_pm_disable_interrupts(dev_priv);
+			intel_runtime_pm_enable_interrupts(dev_priv);
+
+			intel_modeset_init_hw(dev);
+
+			spin_lock_irq(&dev_priv->irq_lock);
+			if (dev_priv->display.hpd_irq_setup)
+				dev_priv->display.hpd_irq_setup(dev);
+			spin_unlock_irq(&dev_priv->irq_lock);
+
+			drm_modeset_lock_all(dev);
+			intel_modeset_setup_hw_state(dev, true);
+			drm_modeset_unlock_all(dev);
+
+			intel_hpd_init(dev_priv);
+		}
 	} else {
 		mutex_unlock(&dev->struct_mutex);
 	}