All operation region accesses are allowed by AML interpreter when AML is
executed, so actually BIOSen are responsible to avoid the operation region
accesses in AML before OSPM has prepared an operation region driver. This
is done via _REG control method. So AML code normally sets a global named
object REGC to 1 when _REG(3, 1) is evaluated.

Then what is ECDT? Quoting from ACPI spec 6.0, 5.2.15 Embedded Controller
Boot Resources Table (ECDT):
 "The presence of this table allows OSPM to provide Embedded Controller
  operation region space access before the namespace has been evaluated."
Spec also suggests a compatible mean to indicate the early EC access
availability:
 Device (EC)
 {
     Name (REGC, Ones)
     Method (_REG, 2)
     {
         If (LEqual (Arg0, 3))
         {
             Store (Arg1, REGC)
         }
     }
     Method (ECAV)
     {
         If (LEqual (REGC, Ones))
         {
             If (LGreaterEqual (_REV, 2))
             {
                 Return (One)
             }
             Else
             {
                 Return (Zero)
             }
         }
         Else
         {
             Return (REGC)
         }
     }
 }
In this way, it allows EC accesses to happen before EC._REG(3, 1) is
invoked.

But ECAV is not the only way practical BIOSen using to indicate the early
EC access availibility, the known variations include:
1. Setting REGC to One in \_SB._INI when _REV >= 2. Since \_SB._INI is the
   first control method evaluated by OSPM during the enumeration, this
   allows EC accesses to happen for the entire enumeration process before
   the namespace EC is enumerated.
2. Initialize REGC to One by default, this even allows EC accesses to
   happen during the table loading.

Linux is now broken around ECDT support during the long term bug fixing
work because it has merged many wrong ECDT bug fixes (see details below).
Linux currently uses namespace EC's settings instead of ECDT settings when
ECDT is detected. This apparently will result in namespace walk and
_CRS/_GPE/_REG evaluations. Such stuffs could only happen after namespace
is ready, while ECDT is purposely to be used before namespace is ready.

The wrong bug fixing story is:
1. Link 1:
   At Linux ACPI early stages, "no _Lxx/_Exx/_Qxx evaluation can happen
   before the namespace is ready" are not ensured by ACPICA core and Linux.
   This is currently ensured by deferred enabling of GPE and defered
   registering of EC query methods (acpi_ec_register_query_methods).
2. Link 2:
   Reporters reported buggy ECDTs, expecting quirks for the platform.
   Originally, the quirk is simple, only doing things with ECDT.
   Bug 9399 and 12461 are platforms (Asus L4R, Asus M6R, MSI MS-171F)
   reported to have wrong ECDT IO port addresses, the port addresses are
   reversed.
   Bug 11880 is a platform (Asus X50GL) reported to have 0 valued port
   addresses, we can see that all EC accesses are protected by ECAV on
   this platform, so actually no early EC accesses is required by this
   platform.
3. Link 3:
   But when the bug fixing developer was requested to provide a handy and
   non-quirk bug fix, he tried to use correct EC settings from namespace
   and broke the spec purpose. We can even see that the developer was
   suffered from many regrssions. One interesting one is 14086, where the
   actual root cause obviously should be: _REG is evaluated too early. But
   unfortunately, the bug is fixed in a totally wrong way.

So everything goes wrong from these commits:
   Commit: c6cb0e87
   Subject: ACPI: EC: Don't trust ECDT tables from ASUS
   Commit: a5032bfd
   Subject: ACPI: EC: Always parse EC device

This patch reverts Linux behavior to simple ECDT quirk support in order to
stop early _CRS/_GPE/_REG evaluations.
For Bug 9399, 12461, since it is reported that the platforms require early
EC accesses, this patch restores the simple ECDT quirks for them.
For Bug 11880, since it is not reported that the platform requires early EC
accesses and its ACPI tables contain correct ECAV, we choose an ECDT
enumeration failure for this platform.

Link 1: https://bugzilla.kernel.org/show_bug.cgi?id=9916
        http://bugzilla.kernel.org/show_bug.cgi?id=10100
        https://lkml.org/lkml/2008/2/25/282
Link 2: https://bugzilla.kernel.org/show_bug.cgi?id=9399
        https://bugzilla.kernel.org/show_bug.cgi?id=12461
        https://bugzilla.kernel.org/show_bug.cgi?id=11880
Link 3: https://bugzilla.kernel.org/show_bug.cgi?id=11884
        https://bugzilla.kernel.org/show_bug.cgi?id=14081
        https://bugzilla.kernel.org/show_bug.cgi?id=14086
        https://bugzilla.kernel.org/show_bug.cgi?id=14446
Link 4: https://bugzilla.kernel.org/show_bug.cgi?id=112911Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Tested-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>