ACPI / EC: EC regression fixes related to EC event stuck

There are 2 regressions reported on bugzilla.

It looks they are related to the modification against the timing of acpi_ec_enable_event() invocation, but they are all due to different root causes.

For link 1, its root cause is: we rely on acpi_ec_suspend/resume() to control the timing of EC event handling enablement, but ECDT is not an ACPI device, thus the PM hooks are not invoked for it.
For link 2, reporter seems to favor a fix that can fix both of the problems:
1. EC event can stuck if there is no triggering source.
2. Post-resume enabling of EC event handling may be too late. But actually the report is only against problem 1 which is known to have a very low and accepted reproduce ratio.

For problem 2, it should has a sympton related to the driver resume order rather than EC event stuck. And its fix should be acpi.ec_freeze_events=Y related. Note acpi.ec_freeze_events=Y is a feature we need to keep for now as:
1. It's reasonable for EC driver to act as an agent for EC event handling while EC transaction is handled by ACPI core handler, thus 1.1. unbind/suspend means suspending EC event handling; 1.2. bind/resume means resuming EC event handling.
2. According to the known EC FW facts, it takes time for EC FW to initialize after boot/resume.

This patchset fixes the root causes of the 2 regressions and keeps the possibility of tuning acpi.ec_freeze_events=Y. Note that PATCH 02 depends on PATCH 01 to be safe for driver unbind.

Lv Zheng (2):
ACPI / EC: Fix a regression related to the triggering source of the EC
event handling
ACPI / EC: Fix a regression related to the PM ops support of ECDT
device

 drivers/acpi/ec.c           | 81 +++++++++++++++++++++++++++++----------------
 drivers/acpi/internal.h     |  1 +
 drivers/acpi/scan.c         | 21 ++++++++++++
 include/acpi/acpi_bus.h     |  1 +
 include/acpi/acpi_drivers.h |  1 +
 5 files changed, 76 insertions(+), 29 deletions(-)

2.7.4