Subject: Item #402: Interrupt Mapping 0.9
Date: Tue, 7 Jan 97 11:11:07 -0800
From: <ron@apple.com>

P1275 Open Firmware Working Group Proposal -- Proposal #402 Ver 1

Title:          map-interrupt procedure change

Author:         Ron Hochsprung

Date:           1/7/97

Ed/Tech:        Technical

Synopsis:
	Updates the map-interrupt procedure to handle common special case
	of direct interrupt-parent.

Doc & Version:  Interrupt Mapping recommended practice 0.9

Problem:

	We have run in to a common case where a device can directly point to
	an interrupt controller (via the "interrupt-parent" property), where
	the interpretation of its "interrupts" property should be the resulting
	unit-interrupt-specifier, without having its unit-address used.

Proposal:

	Change the map-interrupt procedure to include code at the front that
	checks if the device-node contains an "interrupt-parent" property.  If 
so,
	use the parent's node to determine if the unit-address of the device-node
	should be considered part of the unit-interrupt-specifier.

The following code shows the updated procedure:

***** BEGIN CODE *****
procedure map-interrupt( device-node, interrupt-specifier )

	this-node = device-node
	unit-address = valueof( "reg"[0], this-node )
	if present( "interrupt-parent", this-node )
		parent-node = valueof( "interrupt-parent", this-node )
		if present( "#address-cells", parent-node )
			unit-interrupt-specifier = cat( unit-address, interrupt-specifier )
		  else
			unit-interrupt-specifier = interrupt-specifier
		this-node = parent-node

	begin				\ loop up tree until we reach the root

		if present( "interrupt-controller", this-node )
			if present( "interrupt-parent", this-node )
				parent-node = valueof( "interrupt-parent", this-node )
				if present( "#address-cells", parent-node )
					unit-address = valueof( "reg"[0], this-node )
				  else
					unit-address = NULL
				  then
				interrupt-specifier = valueof( "interrupts", this-node )
				unit-interrupt-specifier = cat( unit-address, interrupt-specifier )
				this-node = parent-node
			  else		\ this is the root node, we're done
				return( unit-interrupt-specifier )
			  then

		else			\ not "interrupt-controller"
		if present( "interrupt-map", this-node )	\ we have a mapping to perform
			if present( "interrupt-map-mask", this-node )
				mask = valueof( "interrupt-map-mask" )
				unit-interrupt-specifier = unit-interrupt-specifier & mask
			  then
			init-decode-cells( "interrupt-map", this-node )
			found? = false
			begin
				child-specifier = decode-cells( sizeof( unit-interrupt-specifier ) )
				parent-node = decode-cells( 1 )
				if present( "#address-cells", parent-node )
					#cells = valueof( "#address-cells", parent-node )
				  else
					#cells = 0
				  then
				#cells = #cells + valueof( "#interrupt-cells", parent-node )
				if child-specifier == unit-interrupt-specifier
					found? = true
				  else
					dummy = decode-cells( #cells )
				  then
				until found?
			interrupt-specifier = decode-cells( #cells )
			if present( "#address-cells", parent-node)
				unit-address = valueof( "reg"[0], this-node )
			  else
				unit-address = NULL
			  then
			unit-interrupt-specifier = cat( unit-address, interrupt-specifier )
			this-node = parent-node

        else            \ no "interrupt-map" table
        if present( "interrupt-parent", this-node )
            this-node = valueof( "interrupt-parent", this-node )

        else            \ by default, use our device-tree parent
            this-node = device-tree-parent( this-node )
        then
        again
***** END CODE *****

[ P1275 Item #402 -- Received: Tue Jan  7 11:10:51 PST 1997 ]