Linux内核Device Tree怎么创建

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在Linux内核启动时，内核通过of_platform_populate（）函数，将dts中的device node创建成platform device。为后续和各类驱动的platform driver匹配做准备。

of_platform_populate（）函数在文件drivers/of/platform.c中实现。下面基于RockPI 4A单板的内核代码介绍其调用流程和实现过程。

一、函数调用流程

在Linux内核中，可以使用dump_stack（）函数查看函数的调用流程。

/** * of_platform_populate() - Populate platform_devices from device tree data... #省略部分注释 */int of_platform_populate(struct device_node *root,            const struct of_device_id *matches,            const struct of_dev_auxdata *lookup,            struct device *parent){    struct device_node *child;    int rc = 0;    dump_stack();    ### 打印函数调用的堆栈信息    //1.如果root为NULL，则通过of_find_node_by_path（）查找    root = root ? of_node_get(root) : of_find_node_by_path("/");    if (!root)        return -EINVAL;    //2.遍历dts中的节点    for_each_child_of_node(root, child) {        //3.为每个节点和子节点创建platform device        rc = of_platform_bus_create(child, matches, lookup, parent, true);        ...    }    ...}EXPORT_SYMBOL_GPL(of_platform_populate);

dump_stack（）堆栈信息如下：

[    0.311191] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.154-00036-gcef30e88a9f5-dirty #36[    0.311198] Hardware name: ROCK PI 4A 2 (DT)[    0.311206] Call trace:[    0.311220] [] dump_backtrace+0x0/0x220[    0.311232] [] show_stack+0x24/0x30[    0.311244] [] dump_stack+0x98/0xc0[    0.311258] [] of_platform_populate+0x30/0xb8[    0.311268] [] arm64_device_init+0x30/0x4c[    0.311278] [] do_one_initcall+0x18c/0x194[    0.311290] [] kernel_init_freeable+0x228/0x22c[    0.311301] [] kernel_init+0x18/0x100[    0.311311] [] ret_from_fork+0x10/0x20

从堆栈信息中，可以看出：在arm64_device_init()函数中实现了of_platform_populate（）函数的调用。后续介绍kernel_init（）函数，暂时先留个念想。

注：

arm64_device_init()函数在arch/arm64/kernel/setup.c文件中实现。此时，串口驱动尚未加载，串口日志保存在缓冲区中。由于RK3399是多核，在Linux内核启动时，堆栈信息或其它日志有可能会丢失。在系统启动时，可以增加nosmp配置，关闭其他CPU的加载，保证尽可能多的日志输出。在配置文件/boot/extlinux/extlinux.conf最后增加：

label kernel-debug    kernel /debug/Image    fdt /debug/rk3399-rock-pi-4a.dtb    append earlyprintk console=ttyFIQ0,1500000n8 init=/sbin/init root=PARTUUID=b921b045-1d rw rootwait rootfstype=ext4 nosmp

二、函数实现过程

of_platform_populate（）函数主要通过of_platform_bus_create（）函数创建platform device。为了理解其实现过程，通过printk增加了部分调试日志，代码如下：

/** * of_platform_bus_create() - Create a device for a node and its children. * @bus: device node of the bus to instantiate * @matches: match table for bus nodes * @lookup: auxdata table for matching id and platform_data with device nodes * @parent: parent for new device, or NULL for top level. * @strict: require compatible property * * Creates a platform_device for the provided device_node, and optionally * recursively create devices for all the child nodes. */static int of_platform_bus_create(struct device_node *bus,                  const struct of_device_id *matches,                  const struct of_dev_auxdata *lookup,                  struct device *parent, bool strict){    ...    printk(KERN_ERR"--- name %s \n",bus->name);        //1.判断是否有compatible属性，没有则返回    /* Make sure it has a compatible property */    if (strict && (!of_get_property(bus, "compatible", NULL))) {        printk(KERN_ERR"--- %s() - skipping %s, no compatible prop\n",             __func__, bus->full_name);        return 0;    }    ...    //2.创建platform device    dev = of_platform_device_create_pdata(bus, bus_id, platform_data, parent);    if (!dev || !of_match_node(matches, bus)) {        printk(KERN_ERR"--- no match node\n");        return 0;    }    //3.遍历子节点。如果存在，则创建platform device    for_each_child_of_node(bus, child) {        printk(KERN_ERR"---   create child: %s\n", child->full_name);        rc = of_platform_bus_create(child, matches, lookup, &dev->dev, strict);        if (rc) {            of_node_put(child);            break;        }    }    of_node_set_flag(bus, OF_POPULATED_BUS);    return rc;}

更新内核映像后，截取了部分内核启动日志，如下：

[    0.326151] --- name syscon[    0.326311] ---   create child: /syscon@ff770000/io-domains[    0.326318] --- name io-domains[    0.326458] --- no match node[    0.326466] ---   create child: /syscon@ff770000/usb2-phy@e450[    0.326472] --- name usb2-phy[    0.326627] --- no match node[    0.326635] ---   create child: /syscon@ff770000/usb2-phy@e460[    0.326641] --- name usb2-phy[    0.326791] --- no match node[    0.326798] ---   create child: /syscon@ff770000/phy@f780[    0.326804] --- name phy[    0.326958] --- no match node[    0.326965] ---   create child: /syscon@ff770000/mipi-dphy-rx0[    0.326972] --- name mipi-dphy-rx0[    0.327113] --- no match node[    0.327120] ---   create child: /syscon@ff770000/pvtm[    0.327126] --- name pvtm[    0.327291] --- no match node...                                              ## 省略部分log[    0.330604] --- name display-subsystem        ## drm[    0.330742] --- no match node...

上述日志中的节点名称bus->name和子节点名称child->full_name可在arch/arm64/boot/dts/rockchip/rk3399.dtsi文件中查到：

    grf: syscon@ff770000 {                        ## syscon对应节点名        compatible = "rockchip,rk3399-grf", "syscon", "simple-mfd";        reg = <0x0 0xff770000 0x0 0x10000>;        #address-cells = <1>;        #size-cells = <1>;        io_domains: io-domains {            compatible = "rockchip,rk3399-io-voltage-domain";            status = "disabled";        };        u2phy0: usb2-phy@e450 {                     ## usb2-phy@e450对应子节点名            compatible = "rockchip,rk3399-usb2phy";            reg = <0xe450 0x10>;            clocks = <&cru SCLK_USB2PHY0_REF>;            clock-names = "phyclk";            #clock-cells = <0>;            clock-output-names = "clk_usbphy0_480m";            status = "disabled";            ...        }    }    ...    display_subsystem: display-subsystem {          ## display-subsystem 对应节点名        compatible = "rockchip,display-subsystem";        ports = <&vopl_out>, <&vopb_out>;        clocks = <&cru PLL_VPLL>, <&cru PLL_CPLL>;        clock-names = "hdmi-tmds-pll", "default-vop-pll";        devfreq = <&dmc>;        status = "disabled";    };

在系统启动后，可以在/sys/firmware/devicetree/base路径下查看dts文件节点，在/sys/devices/platform路径下查看platform device。

root@linaro-alip:/sys/firmware/devicetree/base# ls syscon@ff770000/#address-cells  compatible  mipi-dphy-rx0  phandle   pvtm  usb2-phy@e450#size-cells     io-domains  name           phy@f780  reg   usb2-phy@e460root@linaro-alip:/sys/firmware/devicetree/base# ls display-subsystem/clock-names  compatible  logo-memory-region  phandle  routeclocks       devfreq     name                ports    statusroot@linaro-alip:/sys/firmware/devicetree/base#

root@linaro-alip:/sys/devices/platform# ls ff770000.syscon/driver_override                ff770000.syscon:usb2-phy@e460/ff770000.syscon:io-domains/    modaliasff770000.syscon:mipi-dphy-rx0/ of_node/ff770000.syscon:phy@f780/      power/ff770000.syscon:pvtm/          subsystem/ff770000.syscon:usb2-phy@e450/ ueventroot@linaro-alip:/sys/devices/platform# ls display-subsystem/driver           drm       modalias  power      ueventdriver_override  graphics  of_node   subsyste

感谢各位的阅读，以上就是"Linux内核Device Tree怎么创建"的内容了，经过本文的学习后，相信大家对Linux内核Device Tree怎么创建这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是，小编将为大家推送更多相关知识点的文章，欢迎关注！