char: xillybus: add WQ_UNBOUND to alloc_workqueue users

Currently if a user enqueues a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.
This lack of consistency cannot be addressed without refactoring the API.

alloc_workqueue() treats all queues as per-CPU by default, while unbound
workqueues must opt-in via WQ_UNBOUND.

This default is suboptimal: most workloads benefit from unbound queues,
allowing the scheduler to place worker threads where they’re needed and
reducing noise when CPUs are isolated.

This continues the effort to refactor workqueue APIs, which began with
the introduction of new workqueues and a new alloc_workqueue flag in:

commit 128ea9f ("workqueue: Add system_percpu_wq and system_dfl_wq")
commit 930c2ea ("workqueue: Add new WQ_PERCPU flag")

This change adds the WQ_UNBOUND flag to explicitly request
alloc_workqueue() to be unbound, because this specific workload has no
benefit being per-cpu.

With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
must now use WQ_PERCPU.

Once migration is complete, WQ_UNBOUND can be removed and unbound will
become the implicit default.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Acked-by: Eli Billauer <eli.billauer@gmail.com>
Link: https://patch.msgid.link/20251107163755.356187-1-marco.crivellari@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: DispatchCode

drivers/char/xillybus/xillybus_core.c

@@ -1973,7 +1973,7 @@ EXPORT_SYMBOL(xillybus_endpoint_remove);
 
 static int __init xillybus_init(void)
 {
-	xillybus_wq = alloc_workqueue(xillyname, 0, 0);
+	xillybus_wq = alloc_workqueue(xillyname, WQ_UNBOUND, 0);
 	if (!xillybus_wq)
 		return -ENOMEM;
 

drivers/char/xillybus/xillyusb.c

@@ -2163,7 +2163,7 @@ static int xillyusb_probe(struct usb_interface *interface,
 	spin_lock_init(&xdev->error_lock);
 	xdev->in_counter = 0;
 	xdev->in_bytes_left = 0;
-	xdev->workq = alloc_workqueue(xillyname, WQ_HIGHPRI, 0);
+	xdev->workq = alloc_workqueue(xillyname, WQ_HIGHPRI | WQ_UNBOUND, 0);
 
 	if (!xdev->workq) {
 		dev_err(&interface->dev, "Failed to allocate work queue\n");
@@ -2275,7 +2275,7 @@ static int __init xillyusb_init(void)
 {
 	int rc = 0;
 
-	wakeup_wq = alloc_workqueue(xillyname, 0, 0);
+	wakeup_wq = alloc_workqueue(xillyname, WQ_UNBOUND, 0);
 	if (!wakeup_wq)
 		return -ENOMEM;