B3 GPIO changes: new EC -> Host IRQ

[John Watlington]

Paul,
    Having discovered problems with our previously proposed
method of co-generating interrupts on the host, tonight's installment
details a work around restoring a second interrupt line from the EC
to the VX855 (eliminated earlier in the design, and incorrectly  
implemented
then anyway.).

In a previous episode:
The embedded controller (EC) in the laptop communicates a bunch of stuff
to the "host" processor.  It does this through some ports on the I/O  
bus and
and interrupt wire to the host.  Our intrepid code hacker pgf  
proposed that
it would be much easier to support many of the cool features we support
through this EC communciations channel (lid switches, EB mode switches,
gamepad and rotate button presses, etc.) would be easier to support if
we had a separate virtual communications channel with the EC.   This
channel would have an interrupt handler which wasn't in the ACPI code.

Fine, we'll just wire the EC interrupt to another convenient  
interrupt input
on the VX855.   That input turned out to have complicated issues with  
it's
parents, and couldn't be used.   The only "available" inputs are also  
used
to set chip options at "power-on", which is every resume.   As the EC  
interrupt
is frequently asserted at power-up, it would screw up these key  
initializations.

Current proposal:
We will provide a second interrupt from the EC to the host.   This  
interrupt
will go through an input which isn't "owned" by ACPI.   This  
interrupt will
not be asserted unless the system is running (S0).
This interrupt will not be able to "wake" the system, although the EC
may preceed it with an SCI interrupt to wake the system.

This allows this second interrupt to now use one of the available  
inputs.
One slight hitch is that the host control of the WLAN LED will be  
bumped.
This will now be driven solely from the WLAN module as in XO-1.

New GPIO mappings are attached.

Cheers,
wad

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