diff options
author | Linus Torvalds | 2013-09-06 13:30:06 -0700 |
---|---|---|
committer | Linus Torvalds | 2013-09-06 13:30:06 -0700 |
commit | b4b50fd78b1e31989940dfc647e64453d0f7176a (patch) | |
tree | 1a55f110e021c02963b63759f3f18ea7ba3aa228 /Documentation/devicetree/bindings/pci | |
parent | dccfd1e439c11422d7aca0d834b0430d24650e85 (diff) | |
parent | f97c43bbdf8a1ea42477b1a804a48e7e368cb13c (diff) |
Merge tag 'soc-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc
Pull ARM SoC platform changes from Olof Johansson:
"This branch contains mostly additions and changes to platform
enablement and SoC-level drivers. Since there's sometimes a
dependency on device-tree changes, there's also a fair amount of
those in this branch.
Pieces worth mentioning are:
- Mbus driver for Marvell platforms, allowing kernel configuration
and resource allocation of on-chip peripherals.
- Enablement of the mbus infrastructure from Marvell PCI-e drivers.
- Preparation of MSI support for Marvell platforms.
- Addition of new PCI-e host controller driver for Tegra platforms
- Some churn caused by sharing of macro names between i.MX 6Q and 6DL
platforms in the device tree sources and header files.
- Various suspend/PM updates for Tegra, including LP1 support.
- Versatile Express support for MCPM, part of big little support.
- Allwinner platform support for A20 and A31 SoCs (dual and quad
Cortex-A7)
- OMAP2+ support for DRA7, a new Cortex-A15-based SoC.
The code that touches other architectures are patches moving MSI
arch-specific functions over to weak symbols and removal of
ARCH_SUPPORTS_MSI, acked by PCI maintainers"
* tag 'soc-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc: (266 commits)
tegra-cpuidle: provide stub when !CONFIG_CPU_IDLE
PCI: tegra: replace devm_request_and_ioremap by devm_ioremap_resource
ARM: tegra: Drop ARCH_SUPPORTS_MSI and sort list
ARM: dts: vf610-twr: enable i2c0 device
ARM: dts: i.MX51: Add one more I2C2 pinmux entry
ARM: dts: i.MX51: Move pins configuration under "iomuxc" label
ARM: dtsi: imx6qdl-sabresd: Add USB OTG vbus pin to pinctrl_hog
ARM: dtsi: imx6qdl-sabresd: Add USB host 1 VBUS regulator
ARM: dts: imx27-phytec-phycore-som: Enable AUDMUX
ARM: dts: i.MX27: Disable AUDMUX in the template
ARM: dts: wandboard: Add support for SDIO bcm4329
ARM: i.MX5 clocks: Remove optional clock setup (CKIH1) from i.MX51 template
ARM: dts: imx53-qsb: Make USBH1 functional
ARM i.MX6Q: dts: Enable I2C1 with EEPROM and PMIC on Phytec phyFLEX-i.MX6 Ouad module
ARM i.MX6Q: dts: Enable SPI NOR flash on Phytec phyFLEX-i.MX6 Ouad module
ARM: dts: imx6qdl-sabresd: Add touchscreen support
ARM: imx: add ocram clock for imx53
ARM: dts: imx: ocram size is different between imx6q and imx6dl
ARM: dts: imx27-phytec-phycore-som: Fix regulator settings
ARM: dts: i.MX27: Remove clock name from CPU node
...
Diffstat (limited to 'Documentation/devicetree/bindings/pci')
-rw-r--r-- | Documentation/devicetree/bindings/pci/mvebu-pci.txt | 145 | ||||
-rw-r--r-- | Documentation/devicetree/bindings/pci/nvidia,tegra20-pcie.txt | 163 |
2 files changed, 272 insertions, 36 deletions
diff --git a/Documentation/devicetree/bindings/pci/mvebu-pci.txt b/Documentation/devicetree/bindings/pci/mvebu-pci.txt index f8d405897a94..9556e2fedf6d 100644 --- a/Documentation/devicetree/bindings/pci/mvebu-pci.txt +++ b/Documentation/devicetree/bindings/pci/mvebu-pci.txt @@ -1,6 +1,7 @@ * Marvell EBU PCIe interfaces Mandatory properties: + - compatible: one of the following values: marvell,armada-370-pcie marvell,armada-xp-pcie @@ -10,11 +11,49 @@ Mandatory properties: - #interrupt-cells, set to <1> - bus-range: PCI bus numbers covered - device_type, set to "pci" -- ranges: ranges for the PCI memory and I/O regions, as well as the - MMIO registers to control the PCIe interfaces. +- ranges: ranges describing the MMIO registers to control the PCIe + interfaces, and ranges describing the MBus windows needed to access + the memory and I/O regions of each PCIe interface. + +The ranges describing the MMIO registers have the following layout: + + 0x82000000 0 r MBUS_ID(0xf0, 0x01) r 0 s + +where: + + * r is a 32-bits value that gives the offset of the MMIO + registers of this PCIe interface, from the base of the internal + registers. + + * s is a 32-bits value that give the size of this MMIO + registers area. This range entry translates the '0x82000000 0 r' PCI + address into the 'MBUS_ID(0xf0, 0x01) r' CPU address, which is part + of the internal register window (as identified by MBUS_ID(0xf0, + 0x01)). + +The ranges describing the MBus windows have the following layout: + + 0x8t000000 s 0 MBUS_ID(w, a) 0 1 0 + +where: + + * t is the type of the MBus window (as defined by the standard PCI DT + bindings), 1 for I/O and 2 for memory. -In addition, the Device Tree node must have sub-nodes describing each + * s is the PCI slot that corresponds to this PCIe interface + + * w is the 'target ID' value for the MBus window + + * a the 'attribute' value for the MBus window. + +Since the location and size of the different MBus windows is not fixed in +hardware, and only determined in runtime, those ranges cover the full first +4 GB of the physical address space, and do not translate into a valid CPU +address. + +In addition, the device tree node must have sub-nodes describing each PCIe interface, having the following mandatory properties: + - reg: used only for interrupt mapping, so only the first four bytes are used to refer to the correct bus number and device number. - assigned-addresses: reference to the MMIO registers used to control @@ -26,7 +65,8 @@ PCIe interface, having the following mandatory properties: - #address-cells, set to <3> - #size-cells, set to <2> - #interrupt-cells, set to <1> -- ranges, empty property. +- ranges, translating the MBus windows ranges of the parent node into + standard PCI addresses. - interrupt-map-mask and interrupt-map, standard PCI properties to define the mapping of the PCIe interface to interrupt numbers. @@ -47,27 +87,50 @@ pcie-controller { bus-range = <0x00 0xff>; - ranges = <0x82000000 0 0xd0040000 0xd0040000 0 0x00002000 /* Port 0.0 registers */ - 0x82000000 0 0xd0042000 0xd0042000 0 0x00002000 /* Port 2.0 registers */ - 0x82000000 0 0xd0044000 0xd0044000 0 0x00002000 /* Port 0.1 registers */ - 0x82000000 0 0xd0048000 0xd0048000 0 0x00002000 /* Port 0.2 registers */ - 0x82000000 0 0xd004c000 0xd004c000 0 0x00002000 /* Port 0.3 registers */ - 0x82000000 0 0xd0080000 0xd0080000 0 0x00002000 /* Port 1.0 registers */ - 0x82000000 0 0xd0082000 0xd0082000 0 0x00002000 /* Port 3.0 registers */ - 0x82000000 0 0xd0084000 0xd0084000 0 0x00002000 /* Port 1.1 registers */ - 0x82000000 0 0xd0088000 0xd0088000 0 0x00002000 /* Port 1.2 registers */ - 0x82000000 0 0xd008c000 0xd008c000 0 0x00002000 /* Port 1.3 registers */ - 0x82000000 0 0xe0000000 0xe0000000 0 0x08000000 /* non-prefetchable memory */ - 0x81000000 0 0 0xe8000000 0 0x00100000>; /* downstream I/O */ + ranges = + <0x82000000 0 0x40000 MBUS_ID(0xf0, 0x01) 0x40000 0 0x00002000 /* Port 0.0 registers */ + 0x82000000 0 0x42000 MBUS_ID(0xf0, 0x01) 0x42000 0 0x00002000 /* Port 2.0 registers */ + 0x82000000 0 0x44000 MBUS_ID(0xf0, 0x01) 0x44000 0 0x00002000 /* Port 0.1 registers */ + 0x82000000 0 0x48000 MBUS_ID(0xf0, 0x01) 0x48000 0 0x00002000 /* Port 0.2 registers */ + 0x82000000 0 0x4c000 MBUS_ID(0xf0, 0x01) 0x4c000 0 0x00002000 /* Port 0.3 registers */ + 0x82000000 0 0x80000 MBUS_ID(0xf0, 0x01) 0x80000 0 0x00002000 /* Port 1.0 registers */ + 0x82000000 0 0x82000 MBUS_ID(0xf0, 0x01) 0x82000 0 0x00002000 /* Port 3.0 registers */ + 0x82000000 0 0x84000 MBUS_ID(0xf0, 0x01) 0x84000 0 0x00002000 /* Port 1.1 registers */ + 0x82000000 0 0x88000 MBUS_ID(0xf0, 0x01) 0x88000 0 0x00002000 /* Port 1.2 registers */ + 0x82000000 0 0x8c000 MBUS_ID(0xf0, 0x01) 0x8c000 0 0x00002000 /* Port 1.3 registers */ + 0x82000000 0x1 0 MBUS_ID(0x04, 0xe8) 0 1 0 /* Port 0.0 MEM */ + 0x81000000 0x1 0 MBUS_ID(0x04, 0xe0) 0 1 0 /* Port 0.0 IO */ + 0x82000000 0x2 0 MBUS_ID(0x04, 0xd8) 0 1 0 /* Port 0.1 MEM */ + 0x81000000 0x2 0 MBUS_ID(0x04, 0xd0) 0 1 0 /* Port 0.1 IO */ + 0x82000000 0x3 0 MBUS_ID(0x04, 0xb8) 0 1 0 /* Port 0.2 MEM */ + 0x81000000 0x3 0 MBUS_ID(0x04, 0xb0) 0 1 0 /* Port 0.2 IO */ + 0x82000000 0x4 0 MBUS_ID(0x04, 0x78) 0 1 0 /* Port 0.3 MEM */ + 0x81000000 0x4 0 MBUS_ID(0x04, 0x70) 0 1 0 /* Port 0.3 IO */ + + 0x82000000 0x5 0 MBUS_ID(0x08, 0xe8) 0 1 0 /* Port 1.0 MEM */ + 0x81000000 0x5 0 MBUS_ID(0x08, 0xe0) 0 1 0 /* Port 1.0 IO */ + 0x82000000 0x6 0 MBUS_ID(0x08, 0xd8) 0 1 0 /* Port 1.1 MEM */ + 0x81000000 0x6 0 MBUS_ID(0x08, 0xd0) 0 1 0 /* Port 1.1 IO */ + 0x82000000 0x7 0 MBUS_ID(0x08, 0xb8) 0 1 0 /* Port 1.2 MEM */ + 0x81000000 0x7 0 MBUS_ID(0x08, 0xb0) 0 1 0 /* Port 1.2 IO */ + 0x82000000 0x8 0 MBUS_ID(0x08, 0x78) 0 1 0 /* Port 1.3 MEM */ + 0x81000000 0x8 0 MBUS_ID(0x08, 0x70) 0 1 0 /* Port 1.3 IO */ + + 0x82000000 0x9 0 MBUS_ID(0x04, 0xf8) 0 1 0 /* Port 2.0 MEM */ + 0x81000000 0x9 0 MBUS_ID(0x04, 0xf0) 0 1 0 /* Port 2.0 IO */ + + 0x82000000 0xa 0 MBUS_ID(0x08, 0xf8) 0 1 0 /* Port 3.0 MEM */ + 0x81000000 0xa 0 MBUS_ID(0x08, 0xf0) 0 1 0 /* Port 3.0 IO */>; pcie@1,0 { device_type = "pci"; - assigned-addresses = <0x82000800 0 0xd0040000 0 0x2000>; + assigned-addresses = <0x82000800 0 0x40000 0 0x2000>; reg = <0x0800 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0x1 0 1 0 + 0x81000000 0 0 0x81000000 0x1 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 58>; marvell,pcie-port = <0>; @@ -78,12 +141,13 @@ pcie-controller { pcie@2,0 { device_type = "pci"; - assigned-addresses = <0x82001000 0 0xd0044000 0 0x2000>; + assigned-addresses = <0x82001000 0 0x44000 0 0x2000>; reg = <0x1000 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0x2 0 1 0 + 0x81000000 0 0 0x81000000 0x2 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 59>; marvell,pcie-port = <0>; @@ -94,12 +158,13 @@ pcie-controller { pcie@3,0 { device_type = "pci"; - assigned-addresses = <0x82001800 0 0xd0048000 0 0x2000>; + assigned-addresses = <0x82001800 0 0x48000 0 0x2000>; reg = <0x1800 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0x3 0 1 0 + 0x81000000 0 0 0x81000000 0x3 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 60>; marvell,pcie-port = <0>; @@ -110,12 +175,13 @@ pcie-controller { pcie@4,0 { device_type = "pci"; - assigned-addresses = <0x82002000 0 0xd004c000 0 0x2000>; + assigned-addresses = <0x82002000 0 0x4c000 0 0x2000>; reg = <0x2000 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0x4 0 1 0 + 0x81000000 0 0 0x81000000 0x4 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 61>; marvell,pcie-port = <0>; @@ -126,12 +192,13 @@ pcie-controller { pcie@5,0 { device_type = "pci"; - assigned-addresses = <0x82002800 0 0xd0080000 0 0x2000>; + assigned-addresses = <0x82002800 0 0x80000 0 0x2000>; reg = <0x2800 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0x5 0 1 0 + 0x81000000 0 0 0x81000000 0x5 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 62>; marvell,pcie-port = <1>; @@ -142,12 +209,13 @@ pcie-controller { pcie@6,0 { device_type = "pci"; - assigned-addresses = <0x82003000 0 0xd0084000 0 0x2000>; + assigned-addresses = <0x82003000 0 0x84000 0 0x2000>; reg = <0x3000 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0x6 0 1 0 + 0x81000000 0 0 0x81000000 0x6 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 63>; marvell,pcie-port = <1>; @@ -158,12 +226,13 @@ pcie-controller { pcie@7,0 { device_type = "pci"; - assigned-addresses = <0x82003800 0 0xd0088000 0 0x2000>; + assigned-addresses = <0x82003800 0 0x88000 0 0x2000>; reg = <0x3800 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0x7 0 1 0 + 0x81000000 0 0 0x81000000 0x7 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 64>; marvell,pcie-port = <1>; @@ -174,12 +243,13 @@ pcie-controller { pcie@8,0 { device_type = "pci"; - assigned-addresses = <0x82004000 0 0xd008c000 0 0x2000>; + assigned-addresses = <0x82004000 0 0x8c000 0 0x2000>; reg = <0x4000 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0x8 0 1 0 + 0x81000000 0 0 0x81000000 0x8 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 65>; marvell,pcie-port = <1>; @@ -187,14 +257,16 @@ pcie-controller { clocks = <&gateclk 12>; status = "disabled"; }; + pcie@9,0 { device_type = "pci"; - assigned-addresses = <0x82004800 0 0xd0042000 0 0x2000>; + assigned-addresses = <0x82004800 0 0x42000 0 0x2000>; reg = <0x4800 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0x9 0 1 0 + 0x81000000 0 0 0x81000000 0x9 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 99>; marvell,pcie-port = <2>; @@ -205,12 +277,13 @@ pcie-controller { pcie@10,0 { device_type = "pci"; - assigned-addresses = <0x82005000 0 0xd0082000 0 0x2000>; + assigned-addresses = <0x82005000 0 0x82000 0 0x2000>; reg = <0x5000 0 0 0 0>; #address-cells = <3>; #size-cells = <2>; #interrupt-cells = <1>; - ranges; + ranges = <0x82000000 0 0 0x82000000 0xa 0 1 0 + 0x81000000 0 0 0x81000000 0xa 0 1 0>; interrupt-map-mask = <0 0 0 0>; interrupt-map = <0 0 0 0 &mpic 103>; marvell,pcie-port = <3>; diff --git a/Documentation/devicetree/bindings/pci/nvidia,tegra20-pcie.txt b/Documentation/devicetree/bindings/pci/nvidia,tegra20-pcie.txt new file mode 100644 index 000000000000..6b7510775c50 --- /dev/null +++ b/Documentation/devicetree/bindings/pci/nvidia,tegra20-pcie.txt @@ -0,0 +1,163 @@ +NVIDIA Tegra PCIe controller + +Required properties: +- compatible: "nvidia,tegra20-pcie" or "nvidia,tegra30-pcie" +- device_type: Must be "pci" +- reg: A list of physical base address and length for each set of controller + registers. Must contain an entry for each entry in the reg-names property. +- reg-names: Must include the following entries: + "pads": PADS registers + "afi": AFI registers + "cs": configuration space region +- interrupts: A list of interrupt outputs of the controller. Must contain an + entry for each entry in the interrupt-names property. +- interrupt-names: Must include the following entries: + "intr": The Tegra interrupt that is asserted for controller interrupts + "msi": The Tegra interrupt that is asserted when an MSI is received +- pex-clk-supply: Supply voltage for internal reference clock +- vdd-supply: Power supply for controller (1.05V) +- avdd-supply: Power supply for controller (1.05V) (not required for Tegra20) +- bus-range: Range of bus numbers associated with this controller +- #address-cells: Address representation for root ports (must be 3) + - cell 0 specifies the bus and device numbers of the root port: + [23:16]: bus number + [15:11]: device number + - cell 1 denotes the upper 32 address bits and should be 0 + - cell 2 contains the lower 32 address bits and is used to translate to the + CPU address space +- #size-cells: Size representation for root ports (must be 2) +- ranges: Describes the translation of addresses for root ports and standard + PCI regions. The entries must be 6 cells each, where the first three cells + correspond to the address as described for the #address-cells property + above, the fourth cell is the physical CPU address to translate to and the + fifth and six cells are as described for the #size-cells property above. + - The first two entries are expected to translate the addresses for the root + port registers, which are referenced by the assigned-addresses property of + the root port nodes (see below). + - The remaining entries setup the mapping for the standard I/O, memory and + prefetchable PCI regions. The first cell determines the type of region + that is setup: + - 0x81000000: I/O memory region + - 0x82000000: non-prefetchable memory region + - 0xc2000000: prefetchable memory region + Please refer to the standard PCI bus binding document for a more detailed + explanation. +- clocks: List of clock inputs of the controller. Must contain an entry for + each entry in the clock-names property. +- clock-names: Must include the following entries: + "pex": The Tegra clock of that name + "afi": The Tegra clock of that name + "pcie_xclk": The Tegra clock of that name + "pll_e": The Tegra clock of that name + "cml": The Tegra clock of that name (not required for Tegra20) + +Root ports are defined as subnodes of the PCIe controller node. + +Required properties: +- device_type: Must be "pci" +- assigned-addresses: Address and size of the port configuration registers +- reg: PCI bus address of the root port +- #address-cells: Must be 3 +- #size-cells: Must be 2 +- ranges: Sub-ranges distributed from the PCIe controller node. An empty + property is sufficient. +- nvidia,num-lanes: Number of lanes to use for this port. Valid combinations + are: + - Root port 0 uses 4 lanes, root port 1 is unused. + - Both root ports use 2 lanes. + +Example: + +SoC DTSI: + + pcie-controller { + compatible = "nvidia,tegra20-pcie"; + device_type = "pci"; + reg = <0x80003000 0x00000800 /* PADS registers */ + 0x80003800 0x00000200 /* AFI registers */ + 0x90000000 0x10000000>; /* configuration space */ + reg-names = "pads", "afi", "cs"; + interrupts = <0 98 0x04 /* controller interrupt */ + 0 99 0x04>; /* MSI interrupt */ + interrupt-names = "intr", "msi"; + + bus-range = <0x00 0xff>; + #address-cells = <3>; + #size-cells = <2>; + + ranges = <0x82000000 0 0x80000000 0x80000000 0 0x00001000 /* port 0 registers */ + 0x82000000 0 0x80001000 0x80001000 0 0x00001000 /* port 1 registers */ + 0x81000000 0 0 0x82000000 0 0x00010000 /* downstream I/O */ + 0x82000000 0 0xa0000000 0xa0000000 0 0x10000000 /* non-prefetchable memory */ + 0xc2000000 0 0xb0000000 0xb0000000 0 0x10000000>; /* prefetchable memory */ + + clocks = <&tegra_car 70>, <&tegra_car 72>, <&tegra_car 74>, + <&tegra_car 118>; + clock-names = "pex", "afi", "pcie_xclk", "pll_e"; + status = "disabled"; + + pci@1,0 { + device_type = "pci"; + assigned-addresses = <0x82000800 0 0x80000000 0 0x1000>; + reg = <0x000800 0 0 0 0>; + status = "disabled"; + + #address-cells = <3>; + #size-cells = <2>; + + ranges; + + nvidia,num-lanes = <2>; + }; + + pci@2,0 { + device_type = "pci"; + assigned-addresses = <0x82001000 0 0x80001000 0 0x1000>; + reg = <0x001000 0 0 0 0>; + status = "disabled"; + + #address-cells = <3>; + #size-cells = <2>; + + ranges; + + nvidia,num-lanes = <2>; + }; + }; + + +Board DTS: + + pcie-controller { + status = "okay"; + + vdd-supply = <&pci_vdd_reg>; + pex-clk-supply = <&pci_clk_reg>; + + /* root port 00:01.0 */ + pci@1,0 { + status = "okay"; + + /* bridge 01:00.0 (optional) */ + pci@0,0 { + reg = <0x010000 0 0 0 0>; + + #address-cells = <3>; + #size-cells = <2>; + + device_type = "pci"; + + /* endpoint 02:00.0 */ + pci@0,0 { + reg = <0x020000 0 0 0 0>; + }; + }; + }; + }; + +Note that devices on the PCI bus are dynamically discovered using PCI's bus +enumeration and therefore don't need corresponding device nodes in DT. However +if a device on the PCI bus provides a non-probeable bus such as I2C or SPI, +device nodes need to be added in order to allow the bus' children to be +instantiated at the proper location in the operating system's device tree (as +illustrated by the optional nodes in the example above). |