Linux 设备树device tree 使用手册

• 摘要：设备树使用手册Thispagewalksthroughhowtowriteadevicetreeforanewmachine.Itisintendedtoprovideanoverviewofdevicetreeconceptsandhowtheyareusedtodescribeamachine.本文将介绍如何为一个新机器编写设备树。我们准备提供一个有关设备树概念的概述和如何使用这些设备树来描述一个机器。Forafulltechnicaldescriptionofdevic
• 设备树使用手册This page walks through how to write a device tree for a new machine. It is intended to provide an overview of device tree concepts and how they are used to describe a machine. 
  本文将介绍如何为一个新机器编写设备树。我们准备提供一个有关设备树概念的概述和如何使用这些设备树来描述一个机器。 
  For a full technical description of device tree data format, refer to the ePAPR specification. The ePAPR specification covers a lot more detail than the basic topics covered on this page, please refer to it for more advanced 
  usage that isn't covered by this page. 
  完整的设备树数据格式的技术说明书请参考 ePAPR 规范。ePAPR 规范涵盖了比本文基本主题更丰富的细节,要查阅本文没有涉及到的高级用法请参考该规范。

  
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  Contents 目录1 Basic Data Format基本数据格式2 Basic Concepts基本概念 2.1 Sample Machine 2.2 Initial structure 2.3 CPUs 2.4 Node Names 2.5 Devices 2.6 Understanding the compatible Property3 How Addressing Works如何编址 3.1 CPU addressing 3.2 Memory Mapped Devices 3.3 Non Memory Mapped Devices 3.4 Ranges (Address Translation)4 How Interrupts Work中断的工作方式5 Device Specific Data设备特定数据6 Special Nodes特殊的节点 6.1 aliases Node 6.2 chosen Node7 Advanced Topics高级主题 7.1 Advanced Sample Machine 7.2 PCI Host Bridge7.2.1 PCI Bus numbering7.2.2 PCI Address Translation 7.3 Advanced Interrupt Mapping8 Notes附注 
  Basic Data Format 
  基本数据格式 
  ----------------------------------------- 
  The device tree is a simple tree structure of nodes and properties. Properties are key-value pairs, and node may contain both properties and child nodes. For example, the following is a simple tree in the .dts format: 
  设备树是一个包含节点和属性的简单树状结构。属性就是键-值对,而节点可以同时包含属性和子节点。例如,以下就是一个 .dts 格式的简单树:/ {node1 {a-string-property = "A string";a-string-list-property = "first string", "second string";a-byte-data-property = [0x01 0x23 0x34 0x56]; child-node1 {first-child-property;second-child-property = <1>;a-string-property = "Hello, world"; }; child-node2 { }; }; node2 { an-empty-property; a-cell-property = <1 2 3 4>; /* each number (cell) is a uint32 */ child-node1 { }; };}; 
  This tree is obviously pretty useless because it doesn't describe anything, but it does show the structure of nodes an properties. There is: 
  这棵树显然是没什么用的,因为它并没有描述任何东西,但它确实体现了节点的一些属性: 
  ■a single root node: "/" 
  一个单独的根节点:“/” 
  ■a couple of child nodes: "node1" and "node2" 
  两个子节点:“node1”和“node2” 
  ■a couple of children for node1: "child-node1" and "child-node2" 
  两个 node1 的子节点:“child-node1”和“child-node2” 
  ■a bunch of properties scattered through the tree. 
  一堆分散在树里的属性。 
  Properties are simple key-value pairs where the value can either be empty or contain an arbitrary byte stream. While data types are not encoded into the data structure, there are a few fundamental data representations that 
  can be expressed in a device tree source file. 
  属性是简单的键-值对,它的值可以为空或者包含一个任意字节流。虽然数据类型并没有编码进数据结构,但在设备树源文件中任有几个基本的数据表示形式。 
  ■Text strings (null terminated) are represented with double quotes: 
  文本字符串(无结束符)可以用双引号表示:string-property = "a string" 
  ■'Cells' are 32 bit unsigned integers delimited by angle brackets: 
  ‘Cells’是 32 位无符号整数,用尖括号限定:cell-property = <0xbeef 123 0xabcd1234> 
  ■binary data is delimited with square brackets: 
  二进制数据用方括号限定:binary-property = [0x01 0x23 0x45 0x67]; 
  ■Data of differing representations can be concatenated together using a comma: 
  不同表示形式的数据可以使用逗号连在一起:mixed-property = "a string", [0x01 0x23 0x45 0x67], <0x12345678>; 
  ■Commas are also used to create lists of strings: 
  逗号也可用于创建字符串列表:string-list = "red fish", "blue fish"; 
  Basic Concepts 
  基本概念 
  ----------------------------------------- 
  To understand how the device tree is used, we will start with a simple machine and build up a device tree to describe it step by step. 
  我们将以一个简单机开始,然后通过一步步的建立一个描述这个简单机的设备树,来了解如何使用设备树。 
  Sample Machine 
  模型机 
  Consider the following imaginary machine (loosely based on ARM Versatile), manufactured by "Acme" and named "Coyote's Revenge":考虑下面这个假想的机器(大致基于ARM Versatile),制造商为“Acme”,并命名为“Coyote's Revenge”: 
  ■One 32bit ARM CPU 
  一个 32 位 ARM CPU 
  ■processor local bus attached to memory mapped serial port, spi bus controller, i2c controller, interrupt controller, and external bus bridge 
  处理器本地总线连接到内存映射的串行口、spi 总线控制器、i2c 控制器、中断控制器和外部总线桥 
  ■256MB of SDRAM based at 0 
  256MB SDRAM 起始地址为 0 
  ■2 Serial ports based at 0x101F1000 and 0x101F2000 
  两个串口起始地址:0x101F1000 和 0x101F2000 
  ■GPIO controller based at 0x101F3000 
  GPIO 控制器起始地址:0x101F3000 
  ■SPI controller based at 0x10170000 with following devices 
  带有以下设备的 SPI 控制器起始地址:0x10170000 
  ■MMC slot with SS pin attached to GPIO #1 
  MMC 插槽的 SS 管脚连接至 GPIO #1 
  ■External bus bridge with following devices 
  外部总线桥挂载以下设备 
  ■SMC SMC91111 Ethernet device attached to external bus based at 0x10100000 
  SMC SMC91111 以太网设备连接到外部总线,起始地址:0x10100000 
  ■i2c controller based at 0x10160000 with following devices 
  i2c 控制器起始地址:0x10160000,并挂载以下设备 
  ■Maxim DS1338 real time clock. Responds to slave address 1101000 (0x58) 
  Maxim DS1338 实时时钟。响应至从地址 1101000 (0x58) 
  ■64MB of NOR flash based at 0x30000000 
  64MB NOR 闪存起始地址 0x30000000 
  Initial structure 
  初始结构 
  The first step is to lay down a skeleton structure for the machine. This is the bare minimum structure required for a valid device tree. At this stage you want to uniquely identify the machine. 
  第一步就是要为这个模型机构建一个基本结构,这是一个有效的设备树最基本的结构。在这个阶段你需要唯一的标识该机器。/ { compatible = "acme,coyotes-revenge";}; 
  compatible specifies the name of the system. It contains a string in the form " , . It is important to specify the exact device, and to include the manufacturer name to avoid namespace collisions. Since the 
  operating system will use the compatible value to make decisions about how to run on the machine, it is very important to put correct data into this property. 
  compatible 指定了系统的名称。它包含了一个“<制造商>,<型号>”形式的字符串。重要的是要指定一个确切的设备,并且包括制造商的名子,以避免命名空间冲突。由于操作系统会使用 compatible 的值来决定如何在机器上运行,所以正确的设置这个属性变得非常重要。 
  Theoretically, compatible is all the data an OS needs to uniquely identify a machine. If all the machine details are hard coded, then the OS could look specifically for "acme,coyotes-revenge" in the top level compatible property. 
  理论上讲,兼容性(compatible)就是操作系统需要的所有数据都唯一标识一个机器。如果机器的所有细节都是硬编码的,那么操作系统则可以在顶层的 compatible 属性中具体查看“acme,coyotes-revenge”。 
  CPUs 
  中央处理器 
  Next step is to describe for each of the CPUs. A container node named "cpus" is added with a child node for each CPU. In this case the system is a dual-core Cortex A9 system from ARM. 
  接下来就应该描述每个 CPU 了。先添加一个名为“cpus”的容器节点,然后为每个 CPU 分别添加子节点。具体到我们的情况是一个 ARM 的 双核 Cortex A9 系统。/ {compatible = "acme,coyotes-revenge"; 
  cpus { [email protected] {compatible = "arm,cortex-a9"; }; [email protected] { compatible = "arm,cortex-a9"; }; };}; 
  The compatible property in each cpu node is a string that specifies the exact cpu model in the form , , just like the compatible property at the top level. 
  每个 cpu 节点的 compatible 属性是一个“<制造商>,<型号>”形式的字符串,并指定了确切的 cpu,就像顶层的 compatible 属性一样。 
  More properties will be added to the cpu nodes later, but we first need to talk about more of the basic concepts. 
  稍后将会有更多的属性添加进 cpu 节点,但我们先得讨论一些更过的基本概念。 
  Node Names 
  节点名称 
  It is worth taking a moment to talk about naming conventions. Every node must have a name in the form [@ ]. 
  现在应该花点时间来讨论命名约定了。每个节点必须有一个“<名称>[@<设备地址>]”形式的名字。 
  is a simple ascii string and can be up to 31 characters in length. In general, nodes are named according to what kind of device it represents. ie. A node for a 3com Ethernet adapter would be use the name ethernet, not 
  3com509. 
  <名称> 就是一个不超过31位的简单 ascii 字符串。通常,节点的命名应该根据它所体现的是什么样的设备。比如一个 3com 以太网适配器的节点就应该命名为 ethernet,而不应该是 3com509。 
  The unit-address is included if the node describes a device with an address. In general, the unit address is the primary address used to access the device, and is listed in the node's reg property. We'll cover the reg property 
  later in this document. 
  如果该节点描述的设备有一个地址的话就还应该加上设备地址(unit-address)。通常,设备地址就是用来访问该设备的主地址,并且该地址也在节点的 reg 属性中列出。本文档中我们将在稍后涉及到 reg 属性。 
  Sibling nodes must be uniquely named, but it is normal for more than one node to use the same generic name so long as the address is different (ie, [email protected] &; [email protected]). 
  See section 2.2.1 of the ePAPR spec for full details about node naming. 
  同级节点命名必须是唯一的,但只要地址不同,多个节点也可以使用一样的通用名称(例如 [email protected] 和[email protected])。关于节点命名的更多细节请参考 ePAPR 规范 2.2.1 节。 
  Devices 
  设备 
  Every device in the system is represented by a device tree node. The next step is to populate the tree with a node for each of the devices. For now, the new nodes will be left empty until we can talk about how address ranges 
  and irqs are handled. 
  系统中每个设备都表示为一个设备树节点。所以接下来就应该为这个设备树填充设备节点。现在,知道我们讨论如何进行寻址和中断请求如何处理之前这些新节点将一直为空。 
  

  
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  / {compatible = "acme,coyotes-revenge"; 
  cpus { [email protected] {compatible = "arm,cortex-a9";}; [email protected] {compatible = "arm,cortex-a9";};}; 
  [email protected] {compatible = "arm,pl011";}; 
  [email protected] {compatible = "arm,pl011";}; 
  [email protected] {compatible = "arm,pl061";}; 
  [email protected] {compatible = "arm,pl190";}; 
  [email protected] {compatible = "arm,pl022";}; 
  external-bus { [email protected],0 {compatible = "smc,smc91c111";}; 
  [email protected],0 {compatible = "acme,a1234-i2c-bus"; [email protected] { compatible = "maxim,ds1338";};}; 
  [email protected],0 {compatible = "samsung,k8f1315ebm", "cfi-flash";};};};In this tree, a node has been added for each device in the system, and the hierarchy reflects the how devices are connected to the system. ie. devices on the extern bus are children of the external bus node, and i2c devices 
  are children of the i2c bus controller node. In general, the hierarchy represents the view of the system from the perspective of the CPU. 
  在此树中,已经为系统中的每个设备添加了节点,而且这个·层次结构也反映了设备与系统的连接方式。例如,外部总线上的设备就是外部总线节点的子节点,i2c 设备就是 i2c 总线节点的子节点。通常,这个层次结构表现的是 CPU 视角的系统视图。 
  This tree isn't valid at this point. It is missing information about connections between devices. That data will be added later. 
  现在这棵树还是无效的,因为它缺少关于设备之间互联的信息。稍后将添加这些信息。 
  Some things to notice in this tree: 
  在这颗树中,应该注意这些事情: 
  ■Every device node has a compatible property. 
  每个设备节点都拥有一个 compatible 属性。 
  ■The flash node has 2 strings in the compatible property. Read on to the next section to learn why. 
  闪存(flash)节点的 compatible 属性由两个字符串构成。欲知为何,请阅读下一节。 
  ■As mentioned earlier, node names reflect the type of device, not the particular model. See section 2.2.2 of the ePAPR spec for a list of defined generic node names that should be used 
  wherever possible. 
  正如前面所述,节点的命名应当反映设备的类型而不是特定的型号。请查阅 ePAPR 规范第 2.2.2 节里定义的通用节点名,应当优先使用这些节点名。 
  Understanding the compatible Property 
  理解 compatible 属性 
  Every node in the tree that represents a device is required to have the compatible property. compatible is the key an operating system uses to decide which device driver to bind to a device. 
  树中每个表示一个设备的节点都需要一个 compatible 属性。compatible 属性是操作系统用来决定使用哪个设备驱动来绑定到一个设备上的关键因素。 
  compatible is a list of strings. The first string in the list specifies the exact device that the node represents in the form " , ". The following strings represent other devices that the device is compatible 
  with. 
  compatible 是一个字符串列表,之中第一个字符串指定了这个节点所表示的确切的设备,该字符串的格式为:"<制造商>,<型号>"。剩下的字符串的则表示其它与之相兼容的设备。 
  For example, the Freescale MPC8349 System on Chip (SoC) has a serial device which implements the National Semiconductor ns16550 register interface. The compatible property for the MPC8349 serial device should therefore be: 
  compatible = "fsl,mpc8349-uart", "ns16550". In this case, fsl,mpc8349-uart specifies the exact device, and ns16550 states that it is register-level compatible with a National Semiconductor 16550 UART. 
  例如,Freescale MPC8349 片上系统(SoC)拥有一个实现了美国国家半导体 ns16550 的寄存器接口的串行设备,那么 MPC8349 的串行设备的 compatible 属性就应该是:compatible = "fsl,mpc8349-uart", "ns16550"。在这里,mpc8349-uart 指定了确切的设备,而ns16550 则说明这是与美国国家半导体 ns16550UART的寄存器级兼容。 
  Note: ns16550 doesn't have a manufacturer prefix purely for historical reasons. All new compatible values should use the manufacturer prefix. 
  注:ns16550 并没有制造商前缀,这仅仅是历史原因造成的。所有的新 compatible 值都应该使用制造商前缀。 
  This practice allows existing device drivers to be bound to a newer device, while still uniquely identifying the exact hardware. 
  这种做法可以使现有的设备驱动能够绑定到新设备上,并仍然唯一的指定确切的设备。 
  Warning: Don't use wildcard compatible values, like "fsl,mpc83xx-uart" or similar. Silicon vendors will invariably make a change that breaks your wildcard assumptions the moment it is too late to change it. Instead, choose 
  a specific silicon implementations and make all subsequent silicon compatible with it. 
  警告:不要使用带通配符的 compatible 值,比如“fsl,mpc83xx-uart”或类似情况。芯片提供商无不会做出一些能够轻易打破你通配符猜想的变化,这时候在修改已经为时已晚了。相反,应该选择一个特定的芯片然后是所有后续芯片都与之兼容。 
  How Addressing Works 
  如何编址 
  ----------------------------------------- 
  Devices that are addressable use the following properties to encode address information into the device tree: 
  可编址设备使用以下属性将地址信息编码进设备树: 
  ■reg 
  ■#address-cells 
  ■#size-cells 
  Each addressable device gets a reg which is a list of tuples in the form reg = . Each tuple represents an address range used by the device. Each address value is 
  a list of one or more 32 bit integers called cells. Similarly, the length value can either be a list of cells, or empty. 
  每个可编址设备都有一个元组列表的 reg,元组的形式为:reg = <地址1 长度1 [地址2长度2] [地址3长度3] ... >。每个元组都表示一个该设备使用的地址范围。每个地址值是一个或多个 32 位整型数列表,称为 cell。同样,长度值也可以是一个 cell 列表或者为空。 
  Since both the address and length fields are variable of variable size, the #address-cells and #size-cells properties in the parent node are used to state how many cells are in each field. Or in other words, interpreting a 
  reg property correctly requires the parent node's #address-cells and #size-cells values. To see how this all works, lets add the addressing properties to the sample device tree, starting with the CPUs. 
  由于地址和长度字段都是可变大小的变量,那么父节点的 #address-cells 和 #size-cells 属性就用来声明各个字段的 cell 的数量。换句话说,正确解释一个 reg 属性需要用到父节点的 #address-cells 和 #size-cells 的值。要知道这一切是如何运作的,我们将给模型机添加编址属性,就从 CPU 开始。 
  CPU addressing 
  CPU编址 
  The CPU nodes represent the simplest case when talking about addressing. Each CPU is assigned a single unique ID, and there is no size associated with CPU ids. 
  CPU 节点表示了一个关于编址的最简单的例子。每个 CPU 都分配了一个唯一的 ID,并且没有 CPU id 相关的大小信息。cpus { #address-cells = <1>;#size-cells = <0>; [email protected] {compatible = "arm,cortex-a9"; reg = <0>;};[email protected] {compatible = "arm,cortex-a9"; reg = <1>;};}; 
  In the cpus node, #address-cells is set to 1, and #size-cells is set to 0. This means that child reg values are a single uint32 that represent the address with no size field. In this case, the two cpus are assigned addresses 
  0 and 1. #size-cells is 0 for cpu nodes because each cpu is only assigned a single address. 
  在 cpu 节点中,#address-cells 设置为 1,#size-cells 设置为 0。这意味着子节点的 reg 值是一个单一的 uint32,这是一个不包含大小字段的地址,为这两个 cpu 分配的地址是 0 和 1。cpu 节点的 #size-cells 为 0 是因为只为每个 cpu 分配一个单独的地址。 
  You'll also notice that the reg value matches the value in the node name. By convention, if a node has a reg property, then the node name must include the unit-address, which is the first address value in the reg property. 
  你可能还会注意到 reg 的值和节点名字是相同的。按照惯例,如果一个节点有 reg 属性,那么该节点的名字就必须包含设备地址,这个设备地址就是 reg 属性里第一个地址值。 
  Memory Mapped Devices 
  内存映射设备 
  Instead of single address values like found in the cpu nodes, a memory mapped device is assigned a range of addresses that it will respond to. #size-cells is used to state how large the length field is in each child reg tuple. 
  In the following example, each address value is 1 cell (32 bits), and each length value is also 1 cell, which is typical on 32 bit systems. 64 bit machines may use a value of 2 for #address-cells and #size-cells to get 64 bit addressing in the device tree. 
  与 cpu 节点里单一地址值不同,应该分配给内存映射设备一个地址范围。#size-cells 声明每个子节点的 reg 元组中长度字段的大小。在接下来的例子中,每个地址值是 1 cell(32 位),每个长度值也是 1 cell,这是典型的 32 位系统。64 位的机器则可以使用值为 2 的 #address-cells 和 #size-cells 来获得在设备树中的 64 位编址。/ { #address-cells = <1>;#size-cells = <1>; 
  ... 
  [email protected] {compatible = "arm,pl011"; reg = <0x101f0000 0x1000 >;}; 
  [email protected] {compatible = "arm,pl011"; reg = <0x101f2000 0x1000 >;}; 
  [email protected] {compatible = "arm,pl061"; reg = <0x101f3000 0x10000x101f4000 0x0010>;}; 
  [email protected] {compatible = "arm,pl190"; reg = <0x10140000 0x1000 >;}; 
  [email protected] {compatible = "arm,pl022"; reg = <0x10115000 0x1000 >;}; 
  ...}; 
  Each device is assigned a base address, and the size of the region it is assigned. The GPIO device address in this example is assigned two address ranges; 0x101f3000...0x101f3fff and 0x101f4000..0x101f400f. 
  每个设备都被分配了一个基址以及该区域的大小。这个例子中为 GPIO 分配了两个地址范围:0x101f3000...0x101f3fff 和 0x101f4000..0x101f400f。 
  Some devices live on a bus with a different addressing scheme. For example, a device can be attached to an external bus with discrete chip select lines. Since each parent node defines the addressing domain for its children, 
  the address mapping can be chosen to best describe the system. The code below show address assignment for devices attached to the external bus with the chip select number encoded into the address. 
  一些挂在总线上的设备有不同的编址方案。例如一个带独立片选线的设备也可以连接至外部总线。由于父节点会为其子节点定义地址域,所以可以选择不同的地址映射来最恰当的描述该系统。下面的代码展示了设备连接至外部总线并将其片选号编码进地址的地址分配。external-bus { #address-cells = <2>#size-cells = <1>; 
  [email protected],0 {compatible = "smc,smc91c111"; reg = <0 0 0x1000>;}; 
  [email protected],0 {compatible = "acme,a1234-i2c-bus"; reg = <1 0 0x1000>; [email protected] { compatible = "maxim,ds1338";};}; 
  [email protected],0 {compatible = "samsung,k8f1315ebm", "cfi-flash"; reg = <2 0 0x4000000>;};}; 
  The external-bus uses 2 cells for the address value; one for the chip select number, and one for the offset from the base of the chip select. The length field remains as a single cell since only the offset portion of the address 
  needs to have a range. So, in this example, each reg entry contains 3 cells; the chipselect number, the offset, and the length. 
  外部总线的地址值使用了两个 cell,一个用于片选号;另一个则用于片选基址的偏移量。而长度字段则还是单个 cell,这是因为只有地址的偏移部分才需要一个范围量。所以,在这个例子中,每个 reg 项都有三个 cell:片选号、偏移量和长度。 
  Since the address domains are contained to a node and its children, parent nodes are free to define whatever addressing scheme makes sense for the bus. Nodes outside of the immediate parent and child nodes do not normally have 
  to care about the local addressing domain, and addresses have to be mapped to get from one domain to another. 
  由于地址域是包含于一个节点及其子节点的,所以父节点可以自由的定义任何对于该总线来说有意义的编址方案。那些在直接父节点和子节点以外的节点通常不关心本地地址域,而地址应该从一个域映射到另一个域。 
  Non Memory Mapped Devices 
  非内存映射设备 
  Other devices are not memory mapped on the processor bus. They can have address ranges, but they are not directly accessible by the CPU. Instead the parent device's driver would perform indirect access on behalf of the CPU. 
  其他的设备没有被映射到处理机总线上。虽然这些设备可以有一个地址范围,但他们并不是由 CPU 直接访问。取而代之的是,父设备的驱动程序会代表 CPU 执行简介访问。 
  To take the example of i2c devices, each device is assigned an address, but there is no length or range associated with it. This looks much the same as CPU address assignments. 
  以 i2c 设备为例,每个设备都分配了一个地址,但并没有与之关联的长度或范围信息。这看起来和 CPU 的地址分配很像。[email protected],0 {compatible = "acme,a1234-i2c-bus"; #address-cells = <1>; #size-cells = <0>;reg = <1 0 0x1000>;[email protected] { compatible = "maxim,ds1338";reg = <58>;};}; 
  Ranges (Address Translation) 
  范围(地址转换) 
  We've talked about how to assign addresses to devices, but at this point those addresses are only local to the device node. It doesn't yet describe how to map from those address to an address that the CPU can use. 
  我们已经讨论了如何给设备分配地址,但目前来说这些地址还只是设备节点的本地地址,我们还没有描述如何将这些地址映射成 CPU 可使用的地址。 
  The root node always describes the CPU's view of the address space. Child nodes of the root are already using the CPU's address domain, and so do not need any explicit mapping. For example, the [email protected] device is directly 
  assigned the address 0x101f0000. 
  根节点始终描述的是 CPU 视角的地址空间。根节点的子节点已经使用的是 CPU 的地址域,所以它们不需要任何直接映射。例如,[email protected] 设备就是直接分配的 0x101f0000 地址。 
  Nodes that are not direct children of the root do not use the CPU's address domain. In order to get a memory mapped address the device tree must specify how to translate addresses from one domain to another. The ranges property 
  is used for this purpose. 
  那些非根节点直接子节点的节点就没有使用 CPU 地址域。为了得到一个内存映射地址,设备树必须指定从一个域到另一个域地址转换地方法,而 ranges 属性就为此而生。 
  Here is the sample device tree with the ranges property added. 
  下面就是一个添加了 ranges 属性的示例设备树。/ {compatible = "acme,coyotes-revenge";#address-cells = <1>;#size-cells = <1>;...external-bus {#address-cells = <2>#size-cells = <1>; ranges = <0 0 0x101000000x10000 // Chipselect 1, Ethernet1 0 0x101600000x10000 // Chipselect 2, i2c controller2 0 0x300000000x10000000>; // Chipselect 3, NOR Flash 
  [email protected],0 {compatible = "smc,smc91c111";reg = <0 0 0x1000>;}; 
  [email protected],0 {compatible = "acme,a1234-i2c-bus";#address-cells = <1>;#size-cells = <0>;reg = <1 0 0x1000>;[email protected] { compatible = "maxim,ds1338"; reg = <58>;};}; 
  [email protected],0 {compatible = "samsung,k8f1315ebm", "cfi-flash";reg = <2 0 0x4000000>;};};}; 
  ranges is a list of address translations. Each entry in the ranges table is a tuple containing the child address, the parent address, and the size of the region in the child address space. The size of each field is determined 
  by taking the child's #address-cells value, the parent's #address-cells value, and the child's #size-cells value. For the external bus in our example, the child address is 2 cells, the parent address is 1 cell, and the size is also 1 cell. Three ranges are 
  being translated: 
  ranges 是一个地址转换列表。ranges 表中的每一项都是一个包含子地址、父地址和在子地址空间中区域大小的元组。每个字段的值都取决于子节点的 #address-cells 、父节点的 #address-cells 和子节点的 #size-cells。以本例中的外部总线来说,子地址是 2 cell、父地址是 1 cell、区域大小也是 1 cell。那么三个 ranges 被翻译为: 
  Offset 0 from chip select 0 is mapped to address range 0x10100000..0x1010ffff 
  从片选 0 开始的偏移量 0 被映射为地址范围:0x10100000..0x1010ffff 
  Offset 0 from chip select 1 is mapped to address range 0x10160000..0x1016ffff 
  从片选 0 开始的偏移量 1 被映射为地址范围:0x10160000..0x1016ffff 
  Offset 0 from chip select 2 is mapped to address range 0x30000000..0x10000000 
  从片选 0 开始的偏移量 2 被映射为地址范围:0x30000000..0x10000000 
  Alternately, if the parent and child address spaces are identical, then a node can instead add an empty ranges property. The presence of an empty ranges property means addresses in the child address space are mapped 1:1 onto 
  the parent address space. 
  另外,如果父地址空间和子地址空间是相同的,那么该节点可以添加一个空的 range 属性。一个空的 range 属性意味着子地址将被 1:1 映射到父地址空间。 
  You might ask why address translation is used at all when it could all be written with 1:1 mapping. Some busses (like PCI) have entirely different address spaces whose details need to be exposed to the operating system. Others 
  have DMA engines which need to know the real address on the bus. Sometimes devices need to be grouped together because they all share the same software programmable physical address mapping. Whether or not 1:1 mappings should be used depends a lot on the information 
  needed by the Operating system, and on the hardware design. 
  你有可能会问当全都可以设计成 1:1 映射的时候为何还要使用地址转换。答案就是,有一些具有完全不同地址空间的总线(比如 PCI),而它们的细节需要暴露给操作系统。另外一些带有 DMA 引擎的设备需要知道总线上的真实地址。有时有需要将设备组合到一块,因为他们共享相同的软件可编程物理地址映射。是否应该使用 1:1 映射在很大程度上取决于来自操作系统的信息以及硬件设计。 
  You should also notice that there is no ranges property in the [email protected],0 node. The reason for this is that unlike the external bus, devices on the i2c bus are not memory mapped on the CPU's address domain. Instead, the CPU indirectly 
  accesses the [email protected] device via the [email protected],0 device. The lack of a ranges property means that a device cannot be directly accessed by any device other than it's parent. 
  你还应该注意到在 [email protected],0 节点中并没有 range 属性。不同于外部总线,这里的原因是 i2c 总线上的设备并没有被内存映射到 CPU 的地址域。相反,CPU 将通过 [email protected],0 设备间接访问 [email protected] 设备。缺少 ranges 属性意味着这个设备将不能被出他的父设备之外的任何设备直接访问。 
  How Interrupts Work 
  中断如何工作 
  ----------------------------------------- 
  Unlike address range translation which follows the natural structure of the tree, Interrupt signals can originate from and terminate on any device in a machine. Unlike device addressing which is naturally expressed in the device 
  tree, interrupt signals are expressed as links between nodes independent of the tree. Four properties are used to describe interrupt connections: 
  与遵循树的自然结构而进行的地址转换不同,机器上的任何设备都可以发起和终止中断信号。另外地址的编址也不同于中断信号,前者是设备树的自然表示,而后者者表现为独立于设备树结构的节点之间的链接。描述中断连接需要四个属性: 
  ■interrupt-controller - An empty property declaring a node as a device that receives interrupt signals 
  interrupt-controller - 一个空的属性定义该节点作为一个接收中断信号的设备。 
  ■#interrupt-cells - This is a property of the interrupt controller node. It states how many cells are in an interrupt specifier for this interrupt controller (Similar to #address-cells 
  and #size-cells). 
  #interrupt-cells - 这是一个中断控制器节点的属性。它声明了该中断控制器的中断指示符中 cell 的个数(类似于 #address-cells 和 #size-cells)。 
  ■interrupt-parent - A property of a device node containing a phandle to the interrupt controller that it is attached to. Nodes that do not have an interrupt-parent property can also 
  inherit the property from their parent node. 
  interrupt-parent - 这是一个设备节点的属性,包含一个指向该设备连接的中断控制器的 phandle。那些没有 interrupt-parent 的节点则从它们的父节点中继承该属性。 
  ■interrupts - A property of a device node containing a list of interrupt specifiers, one for each interrupt output signal on the device. 
  interrupts - 一个设备节点属性,包含一个中断指示符的列表,对应于该设备上的每个中断输出信号。 
  An interrupt specifier is one or more cells of data (as specified by #interrupt-cells) that specifies which interrupt input the device is attached to. Most devices only have a single interrupt output as shown in the example 
  below, but it is possible to have multiple interrupt outputs on a device. The meaning of an interrupt specifier depends entirely on the binding for the interrupt controller device. Each interrupt controller can decide how many cells it need to uniquely define 
  an interrupt input. 
  中断指示符是一个或多个 cell 的数据(由 #interrupt-cells 指定),这些数据指定了该设备连接至哪些输入中断。在以下的例子中,大部分设备都只有一个输出中断,但也有可能在一个设备上有多个输出中断。一个中断指示符的意义完全取决于与中断控制器设备的 binding。每个中断控制器可以决定使用几个 cell 来唯一的定义一个输入中断。 
  The following code adds interrupt connections to our Coyote's Revenge example machine: 
  下面的代码为我们 Coyote's Revenge 模型机添加了中断连接:

  
  点击(此处)折叠或打开

  / {compatible = "acme,coyotes-revenge";#address-cells = <1>;#size-cells = <1>; interrupt-parent = <∫c>; 
  cpus {#address-cells = <1>;#size-cells = <0>; [email protected] {compatible = "arm,cortex-a9";reg = <0>;};[email protected] {compatible = "arm,cortex-a9";reg = <1>;};}; 
  [email protected] {compatible = "arm,pl011";reg = <0x101f0000 0x1000 >; interrupts = < 1 0 >;}; 
  [email protected] {compatible = "arm,pl011";reg = <0x101f2000 0x1000 >; interrupts = < 2 0 >;}; 
  [email protected] {compatible = "arm,pl061";reg = <0x101f3000 0x10000x101f4000 0x0010>; interrupts = < 3 0 >;}; 
  intc: [email protected] {compatible = "arm,pl190";reg = <0x10140000 0x1000 >; interrupt-controller;#interrupt-cells = <2>;}; 
  [email protected] {compatible = "arm,pl022";reg = <0x10115000 0x1000 >; interrupts = < 4 0 >;}; 
  external-bus {#address-cells = <2>#size-cells = <1>;ranges = <0 0 0x101000000x10000 // Chipselect 1, Ethernet1 0 0x101600000x10000 // Chipselect 2, i2c controller2 0 0x300000000x1000000>; // Chipselect 3, NOR Flash 
  [email protected],0 {compatible = "smc,smc91c111";reg = <0 0 0x1000>; interrupts = < 5 2 >;}; 
  [email protected],0 {compatible = "acme,a1234-i2c-bus";#address-cells = <1>;#size-cells = <0>;reg = <1 0 0x1000>; interrupts = < 6 2 >; [email protected] { compatible = "maxim,ds1338"; reg = <58>;interrupts = < 7 3 >;};}; 
  [email protected],0 {compatible = "samsung,k8f1315ebm", "cfi-flash";reg = <2 0 0x4000000>;};};};Some things to notice: 
  需要注意的事情: 
  ■The machine has a single interrupt controller, [email protected] 
  这个机器只有一个中断控制器: [email protected]。 
  ■The label 'intc:' has been added to the interrupt controller node, and the label was used to assign a phandle to the interrupt-parent property in the root node. This interrupt-parent 
  value becomes the default for the system because all child nodes inherit it unless it is explicitly overridden. 
  中断控制器节点上添加了‘inc:’标签,该标签用于给根节点的 interrupt-parent 属性分配一个 phandle。这个 interrupt-parent 将成为本系统的默认值,因为所有的子节点都将继承它,除非显示覆写这个属性。 
  ■Each device uses an interrupt property to specify a different interrupt input line. 
  每个设备使用 interrupts 属性来不同的中断输入线。 
  ■#interrupt-cells is 2, so each interrupt specifier has 2 cells. This example uses the common pattern of using the first cell to encode the interrupt line number, and the second cell 
  to encode flags such as active high vs. active low, or edge vs. level sensitive. For any given interrupt controller, refer to the controller's binding documentation to learn how the specifier is encoded. 
  #interrupt-cells 是 2,所以每个中断指示符都有 2 个 cell。本例使用一种通用的模式,也就是用第一个 cell 来编码中断线号;然后用第二个 cell 编码标志位,比如高电平/低电平有效,或者边缘/水平触发。对于任何给定的中断控制器,请参考该控制器的 binding 文档以了解指示符如何编码。 
  Device Specific Data 
  设备特定数据 
  ----------------------------------------- 
  Beyond the common properties, arbitrary properties and child nodes can be added to nodes. Any data needed by the operating system can be added as long as some rules are followed. 
  除了通用属性以外,一个节点中可以添加任何属性和子节点。只要遵循一些规则,可以添加任何操作系统所需要的数据。 
  First, new device-specific property names should use a manufacture prefix so that they don't conflict with existing standard property names. 
  首先,新的设备特定属性的名字都应该使用制造商前缀,以避免和现有标准属性名相冲突。 
  Second, the meaning of the properties and child nodes must be documented in a binding so that a device driver author knows how to interpret the data. A binding documents what a particular compatible value means, what properties 
  it should have, what child nodes it might have, and what device it represents. Each unique compatible value should have its own binding (or claim compatibility with another compatible value). Bindings for new devices are documented in this wiki. See the Main 
  Page for a description of the documentation format and review process. 
  其次,属性和子节点的含义必须存档在 binding 文档中,以便设备驱动程序的程序员知道如何解释这些数据。一个 binding 记录了一个特定 compatible 值的意义、应该包含什么样的属性、有可能包含那些子节点、以及它代表了什么样的设备。每个特别的 compatible 值都应该有一个它自己的 binding(或者要求与其他 compatible 值兼容)。新设备的 binding 存档在本 wiki 
  中。请查看主页上的文档格式描述和审核流程。 
  Third, post new bindings for review on the [email protected] mailing list. Reviewing new bindings catches a lot of common mistakes that will cause problems in the future. 
  第三,使用邮件列表 [email protected] 发送新的 binding 以进行审核。新 binding 的审核可以捕获很多可能在以后导致问题的常见错误。 
  Special Nodes 
  特殊节点 
  ----------------------------------------- 
  aliases Node 
  aliases 节点 
  A specific node is normally referenced by the full path, like /external-bus/ [email protected],0, but that gets cumbersome when what a user really wants to know is, "which device is eth0?" The aliases node can be used to assign a short 
  alias to a full device path. For example: 
  引用一个特定的节点通常使用全路径,如 /external-bus/ [email protected],0,但当用户真真想知道的只是“那个设备是 eth0?”时,这样的全路径就变得很冗长。这时,aliases 节点就可以用于指定一个设备全路径的别名。例如:aliases {ethernet0 = ð0;serial0 = &;serial0;}; 
  The operating system is welcome to use the aliases when assigning an identifier to a device. 
  当给一个设备分配一个识别符是操作系统将非常乐意使用别名。 
  You'll notice a new syntax used here. The property = &;label; syntax assigns the full node path referenced by the label as a string property. This is different from the phandle = < &;label >; form used earlier which inserts a 
  phandle value into a cell. 
  在这里你会发现一个新语法。property = &;label;,将作为字符串属性并通过引用标签来指定一个节点的全路径。这与之前的 phandle = < &;label >; 形式不同,这是把一个 phandle 值插入进一个 cell。 
  chosen Node 
  chosen节点 
  The chosen node doesn't represent a real device, but serves as a place for passing data between firmware and the operating system, like boot arguments. Data in the chosen node does not represent the hardware. Typically the 
  chosen node is left empty in .dts source files and populated at boot time. 
  chosen 节点并不代表一个真正的设备,只是作为一个为固件和操作系统之间传递数据的地方,比如引导参数。chosen 节点里的数据也不代表硬件。通常,chosen 节点在 .dts 源文件中为空,并在启动时填充。 
  In our example system, firmware might add the following to the chosen node: 
  在我们的示例系统中,固件可以往 chosen 节点添加以下信息:chosen {bootargs = "root=/dev/nfs rw nfsroot=192.168.1.1 console=ttyS0,115200";}; 
  Advanced Topics 
  高级主题 
  ----------------------------------------- 
  Advanced Sample Machine 
  高级模型机 
  Now that we've got the basics defined, let's add some hardware to the sample machine to discuss some of the more complicated use cases. 
  现在,我们已经掌握了基本的定义,接下来让我们往模型机里添加一些硬件,以讨论一些更复杂的用例。 
  The advanced sample machine adds a PCI host bridge with control registers memory mapped to 0x10180000, and BARs programmed to start above the address 0x80000000. 
  高级模型机添加了一个 PCI 主桥,其控制寄存器映射到内存 0x10180000,并且 BARs 编程至以地址 0x80000000 为起始。 
  Given what we already know about the device tree, we can start with the addition of the following node to describe the PCI host bridge. 
  既然关于设备树我们已经有所了解了,那么我们就从以下所示新增加的节点来介绍 PCI 主桥。 [email protected] {compatible = "arm,versatile-pci-hostbridge", "pci";reg = <0x10180000 0x1000>;interrupts = <8 0>;}; 
  PCI Host Bridge 
  PCI 主桥 
  This section describes the Host/PCI bridge node. 
  本节介绍 Host/PCI 桥节点。 
  Note, some basic knowledge of PCI is assumed in this section. This is NOT a tutorial about PCI, if you need some more in depth information, please read[1]. You can also refer to either ePAPR or the PCI Bus Binding to Open Firmware. 
  A complete working example for a Freescale MPC5200 can be found here. 
  注,本节将假定读者了解 PCI 的一些基本知识。本文并不是 PCI 教程,想要了解更深入的信息,请阅读 [1]。你也可以参考 ePAPR 或 PCI Bus Binding to Open Firmware(http://playground.sun.com/1275/bindings/pci/pci2_1.pdf)。还可以访问