From 15e28df90169d92731a148fca7d948f804296fe6 Mon Sep 17 00:00:00 2001
From: jsg <jsg@openbsd.org>
Date: Sun, 14 Feb 2021 03:42:55 +0000
Subject: [PATCH] correct drm work flush behaviour

Don't set taskq to system_wq in INIT_WORK().  Test if taskq pointer is
non-NULL before calling taskq_barrier() in flush functions.

fixes a black screen on boot problem with 5.10.y drm using nano x1
bisected by jcs@ to
'drm/i915: Always flush the active worker before returning from the wait'
---
 sys/dev/pci/drm/drm_linux.c               | 11 +++++++----
 sys/dev/pci/drm/include/linux/workqueue.h |  5 +++--
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/sys/dev/pci/drm/drm_linux.c b/sys/dev/pci/drm/drm_linux.c
index d400d72ebc9..1fc4db15c86 100644
--- a/sys/dev/pci/drm/drm_linux.c
+++ b/sys/dev/pci/drm/drm_linux.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: drm_linux.c,v 1.77 2021/02/08 08:18:45 mpi Exp $	*/
+/*	$OpenBSD: drm_linux.c,v 1.78 2021/02/14 03:42:55 jsg Exp $	*/
 /*
  * Copyright (c) 2013 Jonathan Gray <jsg@openbsd.org>
  * Copyright (c) 2015, 2016 Mark Kettenis <kettenis@openbsd.org>
@@ -158,7 +158,8 @@ flush_workqueue(struct workqueue_struct *wq)
 	if (cold)
 		return;
 
-	taskq_barrier((struct taskq *)wq);
+	if (wq)
+		taskq_barrier((struct taskq *)wq);
 }
 
 bool
@@ -167,7 +168,8 @@ flush_work(struct work_struct *work)
 	if (cold)
 		return false;
 
-	taskq_barrier(work->tq);
+	if (work->tq)
+		taskq_barrier(work->tq);
 	return false;
 }
 
@@ -184,7 +186,8 @@ flush_delayed_work(struct delayed_work *dwork)
 		ret = true;
 	}
 
-	taskq_barrier(dwork->tq ? dwork->tq : (struct taskq *)system_wq);
+	if (dwork->tq)
+		taskq_barrier(dwork->tq);
 	return ret;
 }
 
diff --git a/sys/dev/pci/drm/include/linux/workqueue.h b/sys/dev/pci/drm/include/linux/workqueue.h
index e2a877d2ab3..703d2f06b9c 100644
--- a/sys/dev/pci/drm/include/linux/workqueue.h
+++ b/sys/dev/pci/drm/include/linux/workqueue.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: workqueue.h,v 1.3 2020/06/08 04:48:15 jsg Exp $	*/
+/*	$OpenBSD: workqueue.h,v 1.4 2021/02/14 03:42:55 jsg Exp $	*/
 /*
  * Copyright (c) 2015 Mark Kettenis
  *
@@ -79,7 +79,7 @@ typedef void (*work_func_t)(struct work_struct *);
 static inline void
 INIT_WORK(struct work_struct *work, work_func_t func)
 {
-	work->tq = (struct taskq *)system_wq;
+	work->tq = NULL;
 	task_set(&work->task, (void (*)(void *))func, work);
 }
 
@@ -139,6 +139,7 @@ INIT_DELAYED_WORK_ONSTACK(struct delayed_work *dwork, work_func_t func)
 static inline bool
 schedule_work(struct work_struct *work)
 {
+	work->tq = (struct taskq *)system_wq;
 	return task_add(work->tq, &work->task);
 }
 
-- 
2.20.1