drm/nouveau: only runtime suspend by default in optimus configuration

The intent was to only enable it by default for optimus, e.g. see the
runtime_idle callback. The suspend callback may be called directly, e.g.
as a result of nouveau_crtc_set_config.
Reported-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/nouveau_drm.c

@@ -858,6 +858,12 @@ static int nouveau_pmops_runtime_suspend(struct device *dev)
 	if (nouveau_runtime_pm == 0)
 		return -EINVAL;
 
+	/* are we optimus enabled? */
+	if (nouveau_runtime_pm == -1 && !nouveau_is_optimus() && !nouveau_is_v1_dsm()) {
+		DRM_DEBUG_DRIVER("failing to power off - not optimus\n");
+		return -EINVAL;
+	}
+
 	nv_debug_level(SILENT);
 	drm_kms_helper_poll_disable(drm_dev);
 	vga_switcheroo_set_dynamic_switch(pdev, VGA_SWITCHEROO_OFF);