drm/i915: disable runtime PM if RC6 is disabled

On VLV we depend on RC6 to save the GT render and media HW context
before going to the D3 state via RPM, so as a preparation for the
VLV RPM support (added in an upcoming patch) disable RPM if RC6 is
disabled.

There is probably a similar dependency on other platforms too, so for
safety require RC6 for those too. For these platforms (SNB, HSW, BDW)
this is then a possible fix.

v2:
- require RC6 for all RPM platforms, not just for VLV (Paulo, Daniel)

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.c

@@ -951,7 +951,7 @@ static int intel_runtime_suspend(struct device *device)
 	struct drm_device *dev = pci_get_drvdata(pdev);
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
-	if (WARN_ON_ONCE(!dev_priv->rps.enabled))
+	if (WARN_ON_ONCE(!(dev_priv->rps.enabled && intel_enable_rc6(dev))))
 		return -ENODEV;
 
 	WARN_ON(!HAS_RUNTIME_PM(dev));

drivers/gpu/drm/i915/intel_pm.c

@@ -6101,6 +6101,15 @@ void intel_init_runtime_pm(struct drm_i915_private *dev_priv)
 
 	pm_runtime_set_active(device);
 
+	/*
+	 * RPM depends on RC6 to save restore the GT HW context, so make RC6 a
+	 * requirement.
+	 */
+	if (!intel_enable_rc6(dev)) {
+		DRM_INFO("RC6 disabled, disabling runtime PM support\n");
+		return;
+	}
+
 	pm_runtime_set_autosuspend_delay(device, 10000); /* 10s */
 	pm_runtime_mark_last_busy(device);
 	pm_runtime_use_autosuspend(device);
@@ -6116,6 +6125,9 @@ void intel_fini_runtime_pm(struct drm_i915_private *dev_priv)
 	if (!HAS_RUNTIME_PM(dev))
 		return;
 
+	if (!intel_enable_rc6(dev))
+		return;
+
 	/* Make sure we're not suspended first. */
 	pm_runtime_get_sync(device);
 	pm_runtime_disable(device);