MPC52xx Device Tree Bindings ---------------------------- (c) 2006 Secret Lab Technologies Ltd Grant Likely I - Introduction ================ Boards supported by the arch/powerpc architecture require device tree be passed by the boot loader to the kernel at boot time. The device tree describes what devices are present on the board and how they are connected. The device tree can either be passed as a binary blob (as described in Documentation/powerpc/booting-without-of.txt), or passed by Open Firmare (IEEE 1275) compatible firmware using an OF compatible client interface API. This document specifies the requirements on the device-tree for mpc52xx based boards. These requirements are above and beyond the details specified in either the OpenFirmware spec or booting-without-of.txt All new mpc52xx-based boards are expected to match this document. In cases where this document is not sufficient to support a new board port, this document should be updated as part of adding the new board support. II - Philosophy =============== The core of this document is naming convention. The whole point of defining this convention is to reduce or eliminate the number of special cases required to support a 52xx board. If all 52xx boards follow the same convention, then generic 52xx support code will work rather than coding special cases for each new board. This section tries to capture the thought process behind why the naming convention is what it is. 1. Node names ------------- There is strong convention/requirements already established for children of the root node. 'cpus' describes the processor cores, 'memory' describes memory, and 'chosen' provides boot configuration. Other nodes are added to describe devices attached to the processor local bus. Following convention already established with other system-on-chip processors, MPC52xx boards must have an 'soc5200' node as a child of the root node. The soc5200 node holds child nodes for all on chip devices. Child nodes are typically named after the configured function. ie. the FEC node is named 'ethernet', and a PSC in uart mode is named 'serial'. 2. device_type property ----------------------- similar to the node name convention above; the device_type reflects the configured function of a device. ie. 'serial' for a uart and 'spi' for an spi controller. However, while node names *should* reflect the configured function, device_type *must* match the configured function exactly. 3. compatible property ---------------------- Since device_type isn't enough to match devices to drivers, there also needs to be a naming convention for the compatible property. Compatible is an list of device descriptions sorted from specific to generic. For the mpc52xx, the required format for each compatible value is -[-]. At the minimum, the list shall contain two items; the first specifying the exact chip, and the second specifying mpc52xx for the chip. ie. ethernet on mpc5200b: compatible = "mpc5200b-ethernet\0mpc52xx-ethernet" The idea here is that most drivers will match to the most generic field in the compatible list (mpc52xx-*), but can also test the more specific field for enabling bug fixes or extra features. Modal devices, like PSCs, also append the configured function to the end of the compatible field. ie. A PSC in i2s mode would specify "mpc52xx-psc-i2s", not "mpc52xx-i2s". This convention is chosen to avoid naming conflicts with non-psc devices providing the same function. For example, "mpc52xx-spi" and "mpc52xx-psc-spi" describe the mpc5200 simple spi device and a PSC spi mode respectively. If the soc device is more generic and present on other SOCs, the compatible property can specify the more generic device type also. ie. mscan: compatible = "mpc5200-mscan\0mpc52xx-mscan\0fsl,mscan"; At the time of writing, exact chip may be either 'mpc5200' or 'mpc5200b'. Device drivers should always try to match as generically as possible. III - Structure =============== The device tree for an mpc52xx board follows the structure defined in booting-without-of.txt with the following additional notes: 0) the root node ---------------- Typical root description node; see booting-without-of 1) The cpus node ---------------- The cpus node follows the basic layout described in booting-without-of. The bus-frequency property holds the XLB bus frequency The clock-frequency property holds the core frequency 2) The memory node ------------------ Typical memory description node; see booting-without-of. 3) The soc5200 node ------------------- This node describes the on chip SOC peripherals. Every mpc52xx based board will have this node, and as such there is a common naming convention for SOC devices. Required properties: name type description ---- ---- ----------- device_type string must be "soc" ranges int should be <0 baseaddr baseaddr+10000> reg int must be Recommended properties: name type description ---- ---- ----------- compatible string should be "-soc\0mpc52xx-soc" ie. "mpc5200b-soc\0mpc52xx-soc" #interrupt-cells int must be <3>. If it is not defined here then it must be defined in every soc device node. bus-frequency int IPB bus frequency in HZ. Clock rate used by most of the soc devices. Defining it here avoids needing it added to every device node. 4) soc5200 child nodes ---------------------- Any on chip SOC devices available to Linux must appear as soc5200 child nodes. Note: in the tables below, '*' matches all values. ie. *-pic would translate to "mpc5200-pic\0mpc52xx-pic" Required soc5200 child nodes: name device_type compatible Description ---- ----------- ---------- ----------- cdm@ cdm *-cmd Clock Distribution pic@ interrupt-controller *-pic need an interrupt controller to boot bestcomm@ dma-controller *-bestcomm 52xx pic also requires the bestcomm device Recommended soc5200 child nodes; populate as needed for your board name device_type compatible Description ---- ----------- ---------- ----------- gpt@ gpt *-gpt General purpose timers rtc@ rtc *-rtc Real time clock mscan@ mscan *-mscan CAN bus controller pci@ pci *-pci PCI bridge serial@ serial *-psc-uart PSC in serial mode i2s@ i2s *-psc-i2s PSC in i2s mode ac97@ ac97 *-psc-ac97 PSC in ac97 mode spi@ spi *-psc-spi PSC in spi mode irda@ irda *-psc-irda PSC in IrDA mode spi@ spi *-spi MPC52xx spi device ethernet@ network *-fec MPC52xx ethernet device ata@ ata *-ata IDE ATA interface i2c@ i2c *-i2c I2C controller usb@ usb-ohci-be *-ohci,ohci-be USB controller xlb@ xlb *-xlb XLB arbritrator IV - Extra Notes ================ 1. Interrupt mapping -------------------- The mpc52xx pic driver splits hardware IRQ numbers into two levels. The split reflects the layout of the PIC hardware itself, which groups interrupts into one of three groups; CRIT, MAIN or PERP. Also, the Bestcomm dma engine has it's own set of interrupt sources which are cascaded off of peripheral interrupt 0, which the driver interprets as a fourth group, SDMA. The interrupts property for device nodes using the mpc52xx pic consists of three cells; L1 := [CRIT=0, MAIN=1, PERP=2, SDMA=3] L2 := interrupt number; directly mapped from the value in the "ICTL PerStat, MainStat, CritStat Encoded Register" level := [LEVEL_HIGH=0, EDGE_RISING=1, EDGE_FALLING=2, LEVEL_LOW=3]