ACPI: EC: Rework flushing of EC work while suspended to idle

The flushing of pending work in the EC driver uses drain_workqueue()
to flush the event handling work that can requeue itself via
advance_transaction(), but this is problematic, because that
work may also be requeued from the query workqueue.

Namely, if an EC transaction is carried out during the execution of
a query handler, it involves calling advance_transaction() which
may queue up the event handling work again.  This causes the kernel
to complain about attempts to add a work item to the EC event
workqueue while it is being drained and worst-case it may cause a
valid event to be skipped.

To avoid this problem, introduce two new counters, events_in_progress
and queries_in_progress, incremented when a work item is queued on
the event workqueue or the query workqueue, respectively, and
decremented at the end of the corresponding work function, and make
acpi_ec_dispatch_gpe() the workqueues in a loop until the both of
these counters are zero (or system wakeup is pending) instead of
calling acpi_ec_flush_work().

At the same time, change __acpi_ec_flush_work() to call
flush_workqueue() instead of drain_workqueue() to flush the event
workqueue.

While at it, use the observation that the work item queued in
acpi_ec_query() cannot be pending at that time, because it is used
only once, to simplify the code in there.

Additionally, clean up a comment in acpi_ec_query() and adjust white
space in acpi_ec_event_processor().

Fixes: f0ac20c3f613 ("ACPI: EC: Fix flushing of pending work")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
index d91b560e8867..54b2be94d23d 100644
--- a/drivers/acpi/internal.h
+++ b/drivers/acpi/internal.h
@@ -183,6 +183,8 @@ struct acpi_ec {
 	struct work_struct work;
 	unsigned long timestamp;
 	unsigned long nr_pending_queries;
+	unsigned int events_in_progress;
+	unsigned int queries_in_progress;
 	bool busy_polling;
 	unsigned int polling_guard;
 };