apple-drm: quiesce disconnected DCPs on suspend, fix resume crash

drm_mode_config_helper_suspend returns -EINVAL when a secondary DCP
(external display) is disconnected, which blocks the entire PM suspend
path. Even if suspend returns 0 anyway, the DCP RTKit firmware keeps
running and generates mailbox IRQs that immediately wake from s2idle.

When the drm suspend helper fails, iterate CRTCs and call
apple_rtkit_quiesce on disconnected DCPs so they stop generating IRQs.
On resume, re-boot them with apple_rtkit_boot and fire a hotplug event.

Also fix the resume path: drm_mode_config_helper_resume crashes on NULL
suspend_state when suspend failed, so check for that and fall back to a
hotplug event instead.

Tested on M1 MacBook Air (J313) with USB-C display, fairydust 6.18.10.

Signed-off-by: areofyl <areofyl@users.noreply.github.com>

Author: areofyl

drivers/gpu/drm/apple/apple_drv.c

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0-only OR MIT
-/* Copyright 2021 Alyssa Rosenzweig */
+/* Copyright 2021 Alyssa Rosenzweig <alyssa@rosenzweig.io> */
 /* Based on meson driver which is
  * Copyright (C) 2016 BayLibre, SAS
  * Author: Neil Armstrong <narmstrong@baylibre.com>
@@ -38,7 +38,11 @@
 #include <drm/drm_vblank.h>
 #include <drm/drm_fixed.h>
 
+#include <linux/soc/apple/rtkit.h>
+
 #include "dcp.h"
+#include "dcp-internal.h"
+#include "connector.h"
 #include "plane.h"
 
 #define DRIVER_NAME     "apple"
@@ -109,8 +113,6 @@ static void apple_crtc_atomic_enable(struct drm_crtc *crtc,
 	if (crtc_state->active_changed && crtc_state->active) {
 		struct apple_crtc *apple_crtc = to_apple_crtc(crtc);
 		dcp_poweron(apple_crtc->dcp);
-		/* Force the CTM to be set on first swap */
-		crtc_state->color_mgmt_changed = true;
 	}
 
 	if (crtc_state->active)
@@ -439,8 +441,9 @@ static int apple_drm_init_dcp(struct device *dev)
 		 * (successfully). Ignoring it should not do any harm now.
 		 * Needs to reevaluated when adding dcpext support.
 		 */
-		if (ret)
+		if (ret) {
 			dev_warn(dev, "DCP[%d] not ready: %d\n", i, ret);
+		}
 	}
 	/* HACK: Wait for dcp* to settle before a modeset */
 	msleep(100);
@@ -627,19 +630,50 @@ MODULE_DEVICE_TABLE(of, of_match);
 static int apple_platform_suspend(struct device *dev)
 {
 	struct apple_drm_private *apple = dev_get_drvdata(dev);
+	struct drm_crtc *crtc;
+	int ret;
 
-	if (apple)
-		return drm_mode_config_helper_suspend(&apple->drm);
+	if (apple) {
+		ret = drm_mode_config_helper_suspend(&apple->drm);
+		if (ret) {
+			dev_warn(dev, "drm suspend helper failed: %d, quiescing inactive DCPs\n", ret);
+			drm_for_each_crtc(crtc, &apple->drm) {
+				struct apple_crtc *acrtc = to_apple_crtc(crtc);
+				struct apple_dcp *dcp = platform_get_drvdata(acrtc->dcp);
+
+				if (dcp && dcp->connector && !dcp->connector->connected && dcp->rtk) {
+					dev_info(dev, "quiescing disconnected DCP %d\n", dcp->index);
+					apple_rtkit_quiesce(dcp->rtk);
+				}
+			}
+		}
+	}
 
 	return 0;
 }
 
 static int apple_platform_resume(struct device *dev)
 {
 	struct apple_drm_private *apple = dev_get_drvdata(dev);
+	struct drm_crtc *crtc;
 
-	if (apple)
+	if (!apple)
+		return 0;
+
+	if (apple->drm.mode_config.suspend_state) {
 		drm_mode_config_helper_resume(&apple->drm);
+	} else {
+		drm_for_each_crtc(crtc, &apple->drm) {
+			struct apple_crtc *acrtc = to_apple_crtc(crtc);
+			struct apple_dcp *dcp = platform_get_drvdata(acrtc->dcp);
+
+			if (dcp && dcp->connector && !dcp->connector->connected && dcp->rtk) {
+				dev_info(dev, "re-booting DCP %d after quiesce\n", dcp->index);
+				apple_rtkit_boot(dcp->rtk);
+			}
+		}
+		drm_kms_helper_hotplug_event(&apple->drm);
+	}
 
 	return 0;
 }
@@ -690,6 +724,6 @@ static void __exit appledrm_unregister(void)
 module_init(appledrm_register);
 module_exit(appledrm_unregister);
 
-MODULE_AUTHOR("Asahi Linux contributors");
+MODULE_AUTHOR("Alyssa Rosenzweig <alyssa@rosenzweig.io>");
 MODULE_DESCRIPTION(DRIVER_DESC);
 MODULE_LICENSE("Dual MIT/GPL");