Xicu component in Flattened device trees

​Xicu is a m->n irq router.

It concentrates 3 types of interrupt sources:

• IPIs (WTI)
• Timers (PTI)
• External IRQ lines (HWI)

These inputs can be filtered independently for each output signal.

MutekH context

In MutekH, we preferably use the Xicu with:

• N IPIs: 1 per processor
• 1 timer
• M Input IRQ lines (as needed)
• N output lines: 1 per processor

MutekH device tree representation

In MutekH device tree, Xicu is quite tricky to reprensent; we can enumerate the following logical devices:

• a (multi) timer
• 1 ICU (with input selection, masking and callbacks) per CPU.

Thus we use the following device tree:

• Xicu root (a timer)
  • Xicu filter for output 0
  • Xicu filter for output 1
  • …

Flattened device tree representation

In FlattenedDeviceTree, the representation follows this logic.

• There is a timer device which is the root
• There is one filter per output line.

xicu@0xd2200000 {
    device_type = "soclib:xicu:root";
    input_lines = <2>;
    ipis = <4>;
    timers = <1>;
    reg = <0xd2200000 0x1000>;

    out@0 {
        device_type = "soclib:xicu:filter";
        parent = &{/xicu@0xd2200000};
        output_line = <0>;
        irq = <&{/cpus/Mips,32@0} 0>;
    };

    out@1 {
        device_type = "soclib:xicu:filter";
        parent = &{/xicu@0xd2200000};
        output_line = <1>;
        irq = <&{/cpus/Mips,32@1} 0>;
    };

    …
};

Timer designation

Timer may be designated by a couple <&{device_path} timer_id>, maximum timer id is defined by the xicu root "timers" property.

Timer may be used in /chosen, like:

chosen {
    console = &{/tty@0xd0200000};
    timer = <&{/xicu@0xd2200000} 0>;
};

Hardware IRQ input routing

As usual, other components route their IRQs to targets; but as the root is a timer device, IRQs must be routed to one of the output filters. Couple is: <&{device_path} input_id>, maximum hardware line id is defined by the xicu root "input_lines" property.

tty@0xd0200000 {
    device_type = "soclib:tty";
    tty_count = <1>;
    reg = <0xd0200000 0x10>;
    irq = <&{/xicu@0xd2200000/out@0} 0>;
};

IPI routing

Likewise, in MutekH, IPIs are handled by the ICU device class. Processors must use xicu filters as IPI controllers. Couple is: <&{device_path} ipi_id>, maximum IPI id is defined by the xicu root "ipis" property.

Mips,32@0 {
    name = "Mips,32";
    device_type = "cpu";
    reg = <0>;
    icudev_type = "cpu:mips";
    ipi = <&{/xicu@0/out@0} 0>;
};