drm/nouveau: don't attempt to schedule hpd_work on headless cards

If the card doesn't have display hardware, hpd_work and hpd_lock are
left uninitialized which causes BUG when attempting to schedule hpd_work
on runtime PM resume.

Fix it by adding headless flag to DRM and skip any hpd if it's set.

Fixes: ae1aadb ("nouveau: don't fail driver load if no display hw present.")
Link: https://gitlab.freedesktop.org/drm/nouveau/-/issues/337
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Reviewed-by: Ben Skeggs <bskeggs@nvidia.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240607221032.25918-1-anarsoul@gmail.com

Author: anarsoul

drivers/gpu/drm/nouveau/dispnv04/disp.c

@@ -68,7 +68,7 @@ nv04_display_fini(struct drm_device *dev, bool runtime, bool suspend)
 	if (nv_two_heads(dev))
 		NVWriteCRTC(dev, 1, NV_PCRTC_INTR_EN_0, 0);
 
-	if (!runtime)
+	if (!runtime && !drm->headless)
 		cancel_work_sync(&drm->hpd_work);
 
 	if (!suspend)

drivers/gpu/drm/nouveau/dispnv50/disp.c

@@ -2680,7 +2680,7 @@ nv50_display_fini(struct drm_device *dev, bool runtime, bool suspend)
 			nv50_mstm_fini(nouveau_encoder(encoder));
 	}
 
-	if (!runtime)
+	if (!runtime && !drm->headless)
 		cancel_work_sync(&drm->hpd_work);
 }
 

drivers/gpu/drm/nouveau/nouveau_display.c

@@ -450,6 +450,9 @@ nouveau_display_hpd_resume(struct drm_device *dev)
 {
 	struct nouveau_drm *drm = nouveau_drm(dev);
 
+	if (drm->headless)
+		return;
+
 	spin_lock_irq(&drm->hpd_lock);
 	drm->hpd_pending = ~0;
 	spin_unlock_irq(&drm->hpd_lock);
@@ -635,7 +638,7 @@ nouveau_display_fini(struct drm_device *dev, bool suspend, bool runtime)
 	}
 	drm_connector_list_iter_end(&conn_iter);
 
-	if (!runtime)
+	if (!runtime && !drm->headless)
 		cancel_work_sync(&drm->hpd_work);
 
 	drm_kms_helper_poll_disable(dev);
@@ -729,6 +732,7 @@ nouveau_display_create(struct drm_device *dev)
 		/* no display hw */
 		if (ret == -ENODEV) {
 			ret = 0;
+			drm->headless = true;
 			goto disp_create_err;
 		}
 

drivers/gpu/drm/nouveau/nouveau_drv.h

@@ -276,6 +276,7 @@ struct nouveau_drm {
 	/* modesetting */
 	struct nvbios vbios;
 	struct nouveau_display *display;
+	bool headless;
 	struct work_struct hpd_work;
 	spinlock_t hpd_lock;
 	u32 hpd_pending;