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1 MPC5200 Device Tree Bindings
2 ----------------------------
4 (c) 2006-2007 Secret Lab Technologies Ltd
5 Grant Likely <grant.likely at secretlab.ca>
7 ********** DRAFT ***********
8 * WARNING: Do not depend on the stability of these bindings just yet.
9 * The MPC5200 device tree conventions are still in flux
10 * Keep an eye on the linuxppc-dev mailing list for more details
11 ********** DRAFT ***********
13 I - Introduction
14 ================
15 Boards supported by the arch/powerpc architecture require device tree be
16 passed by the boot loader to the kernel at boot time. The device tree
17 describes what devices are present on the board and how they are
18 connected. The device tree can either be passed as a binary blob (as
19 described in Documentation/powerpc/booting-without-of.txt), or passed
20 by Open Firmware (IEEE 1275) compatible firmware using an OF compatible
21 client interface API.
23 This document specifies the requirements on the device-tree for mpc5200
24 based boards. These requirements are above and beyond the details
25 specified in either the Open Firmware spec or booting-without-of.txt
27 All new mpc5200-based boards are expected to match this document. In
28 cases where this document is not sufficient to support a new board port,
29 this document should be updated as part of adding the new board support.
31 II - Philosophy
32 ===============
33 The core of this document is naming convention. The whole point of
34 defining this convention is to reduce or eliminate the number of
35 special cases required to support a 5200 board. If all 5200 boards
36 follow the same convention, then generic 5200 support code will work
37 rather than coding special cases for each new board.
39 This section tries to capture the thought process behind why the naming
40 convention is what it is.
42 1. names
43 ---------
44 There is strong convention/requirements already established for children
45 of the root node. 'cpus' describes the processor cores, 'memory'
46 describes memory, and 'chosen' provides boot configuration. Other nodes
47 are added to describe devices attached to the processor local bus.
49 Following convention already established with other system-on-chip
50 processors, 5200 device trees should use the name 'soc5200' for the
51 parent node of on chip devices, and the root node should be its parent.
53 Child nodes are typically named after the configured function. ie.
54 the FEC node is named 'ethernet', and a PSC in uart mode is named 'serial'.
56 2. device_type property
57 -----------------------
58 similar to the node name convention above; the device_type reflects the
59 configured function of a device. ie. 'serial' for a uart and 'spi' for
60 an spi controller. However, while node names *should* reflect the
61 configured function, device_type *must* match the configured function
62 exactly.
64 3. compatible property
65 ----------------------
66 Since device_type isn't enough to match devices to drivers, there also
67 needs to be a naming convention for the compatible property. Compatible
68 is an list of device descriptions sorted from specific to generic. For
69 the mpc5200, the required format for each compatible value is
70 <chip>-<device>[-<mode>]. The OS should be able to match a device driver
71 to the device based solely on the compatible value. If two drivers
72 match on the compatible list; the 'most compatible' driver should be
73 selected.
75 The split between the MPC5200 and the MPC5200B leaves a bit of a
76 conundrum. How should the compatible property be set up to provide
77 maximum compatibility information; but still accurately describe the
78 chip? For the MPC5200; the answer is easy. Most of the SoC devices
79 originally appeared on the MPC5200. Since they didn't exist anywhere
80 else; the 5200 compatible properties will contain only one item;
81 "mpc5200-<device>".
83 The 5200B is almost the same as the 5200, but not quite. It fixes
84 silicon bugs and it adds a small number of enhancements. Most of the
85 devices either provide exactly the same interface as on the 5200. A few
86 devices have extra functions but still have a backwards compatible mode.
87 To express this information as completely as possible, 5200B device trees
88 should have two items in the compatible list;
89 "mpc5200b-<device>\0mpc5200-<device>". It is *strongly* recommended
90 that 5200B device trees follow this convention (instead of only listing
91 the base mpc5200 item).
93 If another chip appear on the market with one of the mpc5200 SoC
94 devices, then the compatible list should include mpc5200-<device>.
96 ie. ethernet on mpc5200: compatible = "mpc5200-ethernet"
97 ethernet on mpc5200b: compatible = "mpc5200b-ethernet\0mpc5200-ethernet"
99 Modal devices, like PSCs, also append the configured function to the
100 end of the compatible field. ie. A PSC in i2s mode would specify
101 "mpc5200-psc-i2s", not "mpc5200-i2s". This convention is chosen to
102 avoid naming conflicts with non-psc devices providing the same
103 function. For example, "mpc5200-spi" and "mpc5200-psc-spi" describe
104 the mpc5200 simple spi device and a PSC spi mode respectively.
106 If the soc device is more generic and present on other SOCs, the
107 compatible property can specify the more generic device type also.
109 ie. mscan: compatible = "mpc5200-mscan\0fsl,mscan";
111 At the time of writing, exact chip may be either 'mpc5200' or
112 'mpc5200b'.
114 Device drivers should always try to match as generically as possible.
116 III - Structure
117 ===============
118 The device tree for an mpc5200 board follows the structure defined in
119 booting-without-of.txt with the following additional notes:
121 0) the root node
122 ----------------
123 Typical root description node; see booting-without-of
125 1) The cpus node
126 ----------------
127 The cpus node follows the basic layout described in booting-without-of.
128 The bus-frequency property holds the XLB bus frequency
129 The clock-frequency property holds the core frequency
131 2) The memory node
132 ------------------
133 Typical memory description node; see booting-without-of.
135 3) The soc5200 node
136 -------------------
137 This node describes the on chip SOC peripherals. Every mpc5200 based
138 board will have this node, and as such there is a common naming
139 convention for SOC devices.
141 Required properties:
142 name type description
143 ---- ---- -----------
144 device_type string must be "soc"
145 ranges int should be <0 baseaddr baseaddr+10000>
146 reg int must be <baseaddr 10000>
147 compatible string mpc5200: "mpc5200-soc"
148 mpc5200b: "mpc5200b-soc\0mpc5200-soc"
149 system-frequency int Fsystem frequency; source of all
150 other clocks.
151 bus-frequency int IPB bus frequency in HZ. Clock rate
152 used by most of the soc devices.
153 #interrupt-cells int must be <3>.
155 Recommended properties:
156 name type description
157 ---- ---- -----------
158 model string Exact model of the chip;
159 ie: model="fsl,mpc5200"
160 revision string Silicon revision of chip
161 ie: revision="M08A"
163 The 'model' and 'revision' properties are *strongly* recommended. Having
164 them presence acts as a bit of a safety net for working around as yet
165 undiscovered bugs on one version of silicon. For example, device drivers
166 can use the model and revision properties to decide if a bug fix should
167 be turned on.
169 4) soc5200 child nodes
170 ----------------------
171 Any on chip SOC devices available to Linux must appear as soc5200 child nodes.
173 Note: The tables below show the value for the mpc5200. A mpc5200b device
174 tree should use the "mpc5200b-<device>\0mpc5200-<device> form.
176 Required soc5200 child nodes:
177 name device_type compatible Description
178 ---- ----------- ---------- -----------
179 cdm@<addr> cdm mpc5200-cmd Clock Distribution
180 pic@<addr> interrupt-controller mpc5200-pic need an interrupt
181 controller to boot
182 bestcomm@<addr> dma-controller mpc5200-bestcomm 5200 pic also requires
183 the bestcomm device
185 Recommended soc5200 child nodes; populate as needed for your board
186 name device_type compatible Description
187 ---- ----------- ---------- -----------
188 gpt@<addr> gpt fsl,mpc5200-gpt General purpose timers
189 rtc@<addr> rtc mpc5200-rtc Real time clock
190 mscan@<addr> mscan mpc5200-mscan CAN bus controller
191 pci@<addr> pci mpc5200-pci PCI bridge
192 serial@<addr> serial mpc5200-psc-uart PSC in serial mode
193 i2s@<addr> sound mpc5200-psc-i2s PSC in i2s mode
194 ac97@<addr> sound mpc5200-psc-ac97 PSC in ac97 mode
195 spi@<addr> spi mpc5200-psc-spi PSC in spi mode
196 irda@<addr> irda mpc5200-psc-irda PSC in IrDA mode
197 spi@<addr> spi mpc5200-spi MPC5200 spi device
198 ethernet@<addr> network mpc5200-fec MPC5200 ethernet device
199 ata@<addr> ata mpc5200-ata IDE ATA interface
200 i2c@<addr> i2c mpc5200-i2c I2C controller
201 usb@<addr> usb-ohci-be mpc5200-ohci,ohci-be USB controller
202 xlb@<addr> xlb mpc5200-xlb XLB arbitrator
204 Important child node properties
205 name type description
206 ---- ---- -----------
207 cell-index int When multiple devices are present, is the
208 index of the device in the hardware (ie. There
209 are 6 PSC on the 5200 numbered PSC1 to PSC6)
210 PSC1 has 'cell-index = <0>'
211 PSC4 has 'cell-index = <3>'
213 5) General Purpose Timer nodes (child of soc5200 node)
214 On the mpc5200 and 5200b, GPT0 has a watchdog timer function. If the board
215 design supports the internal wdt, then the device node for GPT0 should
216 include the empty property 'fsl,has-wdt'.
218 6) PSC nodes (child of soc5200 node)
219 PSC nodes can define the optional 'port-number' property to force assignment
220 order of serial ports. For example, PSC5 might be physically connected to
221 the port labeled 'COM1' and PSC1 wired to 'COM1'. In this case, PSC5 would
222 have a "port-number = <0>" property, and PSC1 would have "port-number = <1>".
224 PSC in i2s mode: The mpc5200 and mpc5200b PSCs are not compatible when in
225 i2s mode. An 'mpc5200b-psc-i2s' node cannot include 'mpc5200-psc-i2s' in the
226 compatible field.
228 IV - Extra Notes
229 ================
231 1. Interrupt mapping
232 --------------------
233 The mpc5200 pic driver splits hardware IRQ numbers into two levels. The
234 split reflects the layout of the PIC hardware itself, which groups
235 interrupts into one of three groups; CRIT, MAIN or PERP. Also, the
236 Bestcomm dma engine has it's own set of interrupt sources which are
237 cascaded off of peripheral interrupt 0, which the driver interprets as a
238 fourth group, SDMA.
240 The interrupts property for device nodes using the mpc5200 pic consists
241 of three cells; <L1 L2 level>
243 L1 := [CRIT=0, MAIN=1, PERP=2, SDMA=3]
244 L2 := interrupt number; directly mapped from the value in the
245 "ICTL PerStat, MainStat, CritStat Encoded Register"
246 level := [LEVEL_HIGH=0, EDGE_RISING=1, EDGE_FALLING=2, LEVEL_LOW=3]
248 2. Shared registers
249 -------------------
250 Some SoC devices share registers between them. ie. the i2c devices use
251 a single clock control register, and almost all device are affected by
252 the port_config register. Devices which need to manipulate shared regs
253 should look to the parent SoC node. The soc node is responsible
254 for arbitrating all shared register access.