[Skiboot] [ppc/pnv9] clarification on the dtb

[Amol]

Hello,

Below is a part of the dtb file as passed on by the skiboot firmware to a
ppc64 pnv9 VM.

The skiboot version is the one shipped with qemu's version
"QEMU emulator version 6.2.50 (v6.2.0-1976-g6629bf78aa)"

/ {
	....
	compatible = "qemu,powernv9\0ibm,powernv";
	model = "IBM PowerNV (emulated by qemu)";
	pciex at 600c3c0000000 {
		compatible = "ibm,power9-pciex\0ibm,ioda3-phb";
		device_type = "pciex";
		....
		#address-cells = <0x03>;
		#size-cells = <0x02>;
		#interrupt-cells = <0x01>;
		interrupt-parent = <0x804e>;
		ranges = <0x2000000 0x00 0x80000000 0x600c0 0x00 0x00
			0x7fff0000>;
		....                 /*  <-------- no interrupt-map HERE */
		pci at 0 {
			interrupts = <0x01>; /* <------------------ HERE */
			#address-cells = <0x03>;
			#size-cells = <0x02>;
			#interrupt-cells = <0x01>;
			interrupt-map-mask = <0x00 0x00 0x00 0x07>;
			interrupt-map =
<0x00 0x00 0x00 0x01 0x804e 0xfeff8 0x01
 0x00 0x00 0x00 0x02 0x804e 0xfeff9 0x01
 0x00 0x00 0x00 0x03 0x804e 0xfeffa 0x01
 0x00 0x00 0x00 0x04 0x804e 0xfeffb 0x01>;
			ranges = <0x2000000 0x00 0x00 0x2000000 0x00 0x00
				0xf0000000 0x00>;
		};
	};

Of interest is the "interrupts = <0x01>;" property of the pci at 0 node. It has
"interrupts = <0x01>" property, which refers to the PCI #INTA. But its parent,
the ioda3 node, does not have the corresponding interrupt-map facility to
map the #INTA over to a descriptor understood/required by the interrupt
controller.

I checked a dtb, linked at [2], seemingly captured from a hardware machine,
and found no such violation at least among the pci nodes. In it, there is
a pci at 0 node with "interrupts = <0x01>", but it does have a parent, another
pci at 0 node, which possesses the interrupt-map mapping required for translation.

I checked the qemu's raw DTB output and found that it does not contain those
pci-related nodes - they are being added by skiboot.

Is such a setup allowed under the dtb spec? The skiboot function which seems to
add the nodes is pci_add_one_device_node or its peers.

Thanks,
Amol

[1] https://elinux.org/Device_Tree_Usage#Advanced_Interrupt_Mapping
[2] https://people.freebsd.org/~jhibbits/p9_vga_out_devtree.txt