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Subject[PATCH v4 1/3] ACPI / EC: Fix possible driver order issue by moving EC event handling earlier
Date
This patch tries to detect EC events earlier after resume, so that if an
event occurred before invoking acpi_ec_unblock_transactions(), it could be
detected by acpi_ec_unblock_transactions() which is the earliest EC driver
call after resume.

However after the noirq stage, if an event ocurred after
acpi_ec_unblock_transactions() and before acpi_ec_resume(), there was no
mean to detect and trigger it, finally it could cause EC event handling
stuck. Thus this patch also adds a detection in acpi_ec_resume(), trying to
recover from the affection of the noirq stage.

The background of the affection:
EC IRQs contain transaction IRQs (OBF/IBF) and event IRQ (SCI_EVT).
1. Transactions are initiated by hosts. The earliest OSPMs execution of
EC transactions is from acpi_ec_transaction(), where the common EC IRQ
handling procedure - advance_transaction() - is initiated from the
task context.
2. Events are initiated by targets. The earliest OSPMs execution of EC
events is from acpi_ec_gpe_handler(), where the common EC IRQ handling
procedure - advance_transaction() - is initiated from the IRQ context.
During suspend/resume noirq stage, IRQ is disabled, advance_transaction()
which detects SCI_EVT can only be invoked from task context - ec_poll().
Thus if there is no EC transaction occurring in this stage, EC driver
cannot detect SCI_EVT. And the worst case is if there is no EC
transaction after resume, EC event handling will stuck (FW flags SCI_EVT,
but there is no triggering source for OS SW to detect it).

Now the final logic is:
1. If ec_freeze_events=Y, event handling is stopped in acpi_ec_suspend(),
restarted in acpi_ec_resume();
2. If ec_freeze_events=N, event handling is stopped in
acpi_ec_block_transactions(), restarted in
acpi_ec_unblock_transactions();
3. In order to handling the conflict of the edge-trigger nature of EC IRQ
and the Linux noirq stage, advance_transaction() is invoked where the
event handling is enabled and the noirq stage is ended.

Known issue:
1. Event ocurred between acpi_ec_unblock_transactions() and
acpi_ec_resume() may still lead to the order issue. This can only be
fixed by adding a periodic detection mechanism during the noirq stage.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Tested-by: Tomislav Ivek <tomislav.ivek@gmail.com>
---
drivers/acpi/ec.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index fdfae6f..3dc4205 100644
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -486,8 +486,11 @@ static inline void __acpi_ec_enable_event(struct acpi_ec *ec)
{
if (!test_and_set_bit(EC_FLAGS_QUERY_ENABLED, &ec->flags))
ec_log_drv("event unblocked");
- if (!test_bit(EC_FLAGS_QUERY_PENDING, &ec->flags))
- advance_transaction(ec);
+ /*
+ * Unconditionally invoke this once after enabling the event
+ * handling mechanism to detect the pending events.
+ */
+ advance_transaction(ec);
}

static inline void __acpi_ec_disable_event(struct acpi_ec *ec)
@@ -945,7 +948,8 @@ static void acpi_ec_start(struct acpi_ec *ec, bool resuming)
if (!resuming) {
acpi_ec_submit_request(ec);
ec_dbg_ref(ec, "Increase driver");
- }
+ } else if (!ec_freeze_events)
+ __acpi_ec_enable_event(ec);
ec_log_drv("EC started");
}
spin_unlock_irqrestore(&ec->lock, flags);
@@ -1929,7 +1933,18 @@ static int acpi_ec_resume(struct device *dev)
struct acpi_ec *ec =
acpi_driver_data(to_acpi_device(dev));

- acpi_ec_enable_event(ec);
+ if (ec_freeze_events)
+ acpi_ec_enable_event(ec);
+ else {
+ /*
+ * Though whether there is an event pending has been
+ * checked in acpi_ec_unblock_transactions() when
+ * ec_freeze_events=N, check it one more time after noirq
+ * stage to detect events occurred after
+ * acpi_ec_unblock_transactions().
+ */
+ advance_transaction(ec);
+ }
return 0;
}
#endif
--
2.7.4
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