1* SPEAr Shared IRQ layer (shirq)
2
3SPEAr3xx architecture includes shared/multiplexed irqs for certain set
4of devices. The multiplexor provides a single interrupt to parent
5interrupt controller (VIC) on behalf of a group of devices.
6
7There can be multiple groups available on SPEAr3xx variants but not
8exceeding 4. The number of devices in a group can differ, further they
9may share same set of status/mask registers spanning across different
10bit masks. Also in some cases the group may not have enable or other
11registers. This makes software little complex.
12
13A single node in the device tree is used to describe the shared
14interrupt multiplexor (one node for all groups). A group in the
15interrupt controller shares config/control registers with other groups.
16For example, a 32-bit interrupt enable/disable config register can
17accommodate up to 4 interrupt groups.
18
19Required properties:
20  - compatible: should be, either of
21     - "st,spear300-shirq"
22     - "st,spear310-shirq"
23     - "st,spear320-shirq"
24  - interrupt-controller: Identifies the node as an interrupt controller.
25  - #interrupt-cells: should be <1> which basically contains the offset
26    (starting from 0) of interrupts for all the groups.
27  - reg: Base address and size of shirq registers.
28  - interrupts: The list of interrupts generated by the groups which are
29    then connected to a parent interrupt controller. Each group is
30    associated with one of the interrupts, hence number of interrupts (to
31    parent) is equal to number of groups. The format of the interrupt
32    specifier depends in the interrupt parent controller.
33
34Example:
35
36The following is an example from the SPEAr320 SoC dtsi file.
37
38shirq: interrupt-controller@b3000000 {
39	compatible = "st,spear320-shirq";
40	reg = <0xb3000000 0x1000>;
41	interrupts = <28 29 30 1>;
42	#interrupt-cells = <1>;
43	interrupt-controller;
44};
45