platform/surface: aggregator: Allow completion work-items to be executed in parallel

[ Upstream commit 539e0a7f91 ]

Currently, event completion work-items are restricted to be run strictly
in non-parallel fashion by the respective workqueue. However, this has
lead to some problems:

In some instances, the event notifier function called inside this
completion workqueue takes a non-negligible amount of time to execute.
One such example is the battery event handling code (surface_battery.c),
which can result in a full battery information refresh, involving
further synchronous communication with the EC inside the event handler.
This is made worse if the communication fails spuriously, generally
incurring a multi-second timeout.

Since the event completions are run strictly non-parallel, this blocks
other events from being propagated to the respective subsystems. This
becomes especially noticeable for keyboard and touchpad input, which
also funnel their events through this system. Here, users have reported
occasional multi-second "freezes".

Note, however, that the event handling system was never intended to run
purely sequentially. Instead, we have one work struct per EC/SAM
subsystem, processing the event queue for that subsystem. These work
structs were intended to run in parallel, allowing sequential processing
of work items for each subsystem but parallel processing of work items
across subsystems.

The only restriction to this is the way the workqueue is created.
Therefore, replace create_workqueue() with alloc_workqueue() and do not
restrict the maximum number of parallel work items to be executed on
that queue, resolving any cross-subsystem blockage.

Fixes: c167b9c7e3 ("platform/surface: Add Surface Aggregator subsystem")
Link: https://github.com/linux-surface/linux-surface/issues/1026
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20230525210110.2785470-1-luzmaximilian@gmail.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/platform/surface/aggregator/controller.c

@@ -825,7 +825,7 @@ static int ssam_cplt_init(struct ssam_cplt *cplt, struct device *dev)
 
 	cplt->dev = dev;
 
-	cplt->wq = create_workqueue(SSAM_CPLT_WQ_NAME);
+	cplt->wq = alloc_workqueue(SSAM_CPLT_WQ_NAME, WQ_UNBOUND | WQ_MEM_RECLAIM, 0);
 	if (!cplt->wq)
 		return -ENOMEM;