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>

1 files changed, 13 insertions, 1 deletions

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index 79817ce164c1..9d4761d2f6b7 100644
--- 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);