drm/amd/display: Fix system hang after multiple hotplugs (v3)

[Why]
mutex_lock() was introduced in dm_disable_vblank(), which could
be called in an IRQ context. Waiting in IRQ would cause issues
like kernel lockup, etc.

[How]
Handle code that requires mutex lock on a different thread.

v2: squash in compilation fix without CONFIG_DRM_AMD_DC_DCN (Alex)
v3: squash in warning fix (Wei)

Signed-off-by: Qingqing Zhuo <[e-mail]>
Acked-by: Bindu Ramamurthy <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
Cc: [e-mail]

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

···
 
 }
 #endif
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+static void event_mall_stutter(struct work_struct *work)
+{
 
+	struct vblank_workqueue *vblank_work = container_of(work, struct vblank_workqueue, mall_work);
+	struct amdgpu_display_manager *dm = vblank_work->dm;
+
+	mutex_lock(&dm->dc_lock);
+
+	if (vblank_work->enable)
+		dm->active_vblank_irq_count++;
+	else
+		dm->active_vblank_irq_count--;
+
+
+	dc_allow_idle_optimizations(
+		dm->dc, dm->active_vblank_irq_count == 0 ? true : false);
+
+	DRM_DEBUG_DRIVER("Allow idle optimizations (MALL): %d\n", dm->active_vblank_irq_count == 0);
+
+
+	mutex_unlock(&dm->dc_lock);
+}
+
+static struct vblank_workqueue *vblank_create_workqueue(struct amdgpu_device *adev, struct dc *dc)
+{
+
+	int max_caps = dc->caps.max_links;
+	struct vblank_workqueue *vblank_work;
+	int i = 0;
+
+	vblank_work = kcalloc(max_caps, sizeof(*vblank_work), GFP_KERNEL);
+	if (ZERO_OR_NULL_PTR(vblank_work)) {
+		kfree(vblank_work);
+		return NULL;
+	}
+
+	for (i = 0; i < max_caps; i++)
+		INIT_WORK(&vblank_work[i].mall_work, event_mall_stutter);
+
+	return vblank_work;
+}
+#endif
 static int amdgpu_dm_init(struct amdgpu_device *adev)
 {
 	struct dc_init_data init_data;
···
 
 	mutex_init(&adev->dm.dc_lock);
 	mutex_init(&adev->dm.audio_lock);
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+	spin_lock_init(&adev->dm.vblank_lock);
+#endif
 
 	if(amdgpu_dm_irq_init(adev)) {
 		DRM_ERROR("amdgpu: failed to initialize DM IRQ support.\n");
···
 				adev->dm.freesync_module);
 
 	amdgpu_dm_init_color_mod();
+
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+	if (adev->dm.dc->caps.max_links > 0) {
+		adev->dm.vblank_workqueue = vblank_create_workqueue(adev, adev->dm.dc);
+
+		if (!adev->dm.vblank_workqueue)
+			DRM_ERROR("amdgpu: failed to initialize vblank_workqueue.\n");
+		else
+			DRM_DEBUG_DRIVER("amdgpu: vblank_workqueue init done %p.\n", adev->dm.vblank_workqueue);
+	}
+#endif
 
 #ifdef CONFIG_DRM_AMD_DC_HDCP
 	if (adev->dm.dc->caps.max_links > 0 && adev->asic_type >= CHIP_RAVEN) {
···
 	struct amdgpu_crtc *acrtc = to_amdgpu_crtc(crtc);
 	struct amdgpu_device *adev = drm_to_adev(crtc->dev);
 	struct dm_crtc_state *acrtc_state = to_dm_crtc_state(crtc->state);
+#if defined(CONFIG_DRM_AMD_DC_DCN)
 	struct amdgpu_display_manager *dm = &adev->dm;
+	unsigned long flags;
+#endif
 	int rc = 0;
 
 	if (enable) {
···
 	if (amdgpu_in_reset(adev))
 		return 0;
 
-	mutex_lock(&dm->dc_lock);
-
-	if (enable)
-		dm->active_vblank_irq_count++;
-	else
-		dm->active_vblank_irq_count--;
-
 #if defined(CONFIG_DRM_AMD_DC_DCN)
-	dc_allow_idle_optimizations(
-		adev->dm.dc, dm->active_vblank_irq_count == 0 ? true : false);
-
-	DRM_DEBUG_DRIVER("Allow idle optimizations (MALL): %d\n", dm->active_vblank_irq_count == 0);
+	spin_lock_irqsave(&dm->vblank_lock, flags);
+	dm->vblank_workqueue->dm = dm;
+	dm->vblank_workqueue->otg_inst = acrtc->otg_inst;
+	dm->vblank_workqueue->enable = enable;
+	spin_unlock_irqrestore(&dm->vblank_lock, flags);
+	schedule_work(&dm->vblank_workqueue->mall_work);
 #endif
-
-	mutex_unlock(&dm->dc_lock);
 
 	return 0;
 }

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h

···
 };
 
 /**
+ * struct vblank_workqueue - Works to be executed in a separate thread during vblank
+ * @mall_work: work for mall stutter
+ * @dm: amdgpu display manager device
+ * @otg_inst: otg instance of which vblank is being set
+ * @enable: true if enable vblank
+ */
+struct vblank_workqueue {
+	struct work_struct mall_work;
+	struct amdgpu_display_manager *dm;
+	int otg_inst;
+	bool enable;
+};
+
+/**
  * struct amdgpu_dm_backlight_caps - Information about backlight
  *
  * Describe the backlight support for ACPI or eDP AUX.
···
 	struct mutex audio_lock;
 
 	/**
+	 * @vblank_work_lock:
+	 *
+	 * Guards access to deferred vblank work state.
+	 */
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+	spinlock_t vblank_lock;
+#endif
+
+	/**
 	 * @audio_component:
 	 *
 	 * Used to notify ELD changes to sound driver.
···
 	struct mod_freesync *freesync_module;
 #ifdef CONFIG_DRM_AMD_DC_HDCP
 	struct hdcp_workqueue *hdcp_workqueue;
+#endif
+
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+	struct vblank_workqueue *vblank_workqueue;
 #endif
 
 	struct drm_atomic_state *cached_state;