ACPI / EC: Fix a code coverity issue when QR_EC transactions are failed.

When the QR_EC transaction fails, the EC_FLAGS_QUERY_PENDING flag prevents
the event handling work queue from being scheduled again.

Though there shouldn't be failed QR_EC transactions, and this gap was
efficiently used for catching and learning the SCI_EVT clearing timing
compliance issues, we need to fix this as we are not fully compatible
with all platforms/Windows to handle SCI_EVT clearing timing correctly.
Fixing this gives the EC driver the chances to recover from a state machine
failure.

So this patch fixes this issue. When nr_pending_queries drops to 0, it
clears EC_FLAGS_QUERY_PENDING at the proper position for different modes in
order to ensure that the SCI_EVT handling can proceed.

In order to be clearer for future ec_event_clearing modes, all checks in
this patch are written in the inclusive style, not the exclusive style.

Cc: 3.16+ <stable@vger.kernel.org> # 3.16+
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index 79817ce164c17bee4480c9259607efc98f1095f4..9d4761d2f6b77b82f10dda7027c707d4e241895c 100644 (file)
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -512,7 +512,8 @@ static void advance_transaction(struct acpi_ec *ec)
         */
        if (!t || !(t->flags & ACPI_EC_COMMAND_POLL)) {
                if (ec_event_clearing == ACPI_EC_EVT_TIMING_EVENT &&
-                   test_bit(EC_FLAGS_QUERY_GUARDING, &ec->flags)) {
+                   (!ec->nr_pending_queries ||
+                    test_bit(EC_FLAGS_QUERY_GUARDING, &ec->flags))) {
                        clear_bit(EC_FLAGS_QUERY_GUARDING, &ec->flags);
                        acpi_ec_complete_query(ec);
                }
@@ -1065,6 +1066,17 @@ static void acpi_ec_event_handler(struct work_struct *work)
                (void)acpi_ec_query(ec, NULL);
                spin_lock_irqsave(&ec->lock, flags);
                ec->nr_pending_queries--;
+               /*
+                * Before exit, make sure that this work item can be
+                * scheduled again. There might be QR_EC failures, leaving
+                * EC_FLAGS_QUERY_PENDING uncleared and preventing this work
+                * item from being scheduled again.
+                */
+               if (!ec->nr_pending_queries) {
+                       if (ec_event_clearing == ACPI_EC_EVT_TIMING_STATUS ||
+                           ec_event_clearing == ACPI_EC_EVT_TIMING_QUERY)
+                               acpi_ec_complete_query(ec);
+               }
        }
        spin_unlock_irqrestore(&ec->lock, flags);