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0013_dtoverlay.md

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dtoverlay

分析设备树overlay功能，和上篇文档一样

参考文档

Source Code

https://github.com/raspberrypi/userland/tree/master/host_applications/linux/apps/dtoverlay

Linux Overlays Dynamically

  • 查看内核配置挂在点 
    pi@raspberrypi:~ $ mount | grep config
configfs on /sys/kernel/config type configfs (rw,relatime)
    • mount -t configfs none /sys/kernel/config
  • 查看目录 
    pi@raspberrypi:~ $ ls /sys/kernel/config
device-tree  usb_gadget
  • overlays dtparam 
    pi@raspberrypi:~ $ ls /sys/kernel/config/device-tree/overlays/
0_dtparam
pi@raspberrypi:~ $ ls /sys/kernel/config/device-tree/overlays/0_dtparam/
dtbo  path  status
  • sudo dtparam -v i2c_arm=on 
    pi@raspberrypi:~/zengjf/copy $ sudo dtparam -v i2c_arm=on
run_cmd: which dtoverlay-pre >/dev/null 2>&1 && dtoverlay-pre
run_cmd: dtc -I fs -O dtb -o '/tmp/.dtoverlays/base.dtb' /proc/device-tree 1>/dev/null 2>&1
DTOVERLAY[debug]: Found override i2c_arm
DTOVERLAY[debug]:   override i2c_arm: string target 'status'
DTOVERLAY[debug]: delete_node(/__symbols__)
DTOVERLAY[debug]: Wrote 162 bytes to '/tmp/.dtoverlays/0_dtparam.dtbo'
DTOVERLAY[debug]: Wrote 174 bytes to '/sys/kernel/config/device-tree/overlays/0_dtparam/dtbo'
run_cmd: which dtoverlay-post >/dev/null 2>&1 && dtoverlay-post
  • dtc -I dtb -O dts -o ~/zengjf/0_dtparam.dts 0_dtparam.dtbo
  • dtc -I dtb -O dts -o ~/zengjf/base.dts base.dtb
  • rpi dts: https://github.com/raspberrypi/linux/tree/rpi-4.19.y/arch/arm/boot/dts/overlays

dtparam/dtoverlay

  • 两者区别： 
    pi@raspberrypi:/proc/device-tree $ which dtparam
/usr/bin/dtparam
pi@raspberrypi:/proc/device-tree $ ls -al /usr/bin/dtparam
lrwxrwxrwx 1 root root 21 Nov 12 17:26 /usr/bin/dtparam -> /opt/vc/bin/dtoverlay
pi@raspberrypi:/proc/device-tree $ ls -al /usr/bin/dtoverlay
lrwxrwxrwx 1 root root 21 Nov 12 17:26 /usr/bin/dtoverlay -> /opt/vc/bin/dtoverlay
  • 帮助文档： 
    static void usage(void)
{
    printf("Usage:\n");
    if (strcmp(cmd_name, "dtparam") == 0)
    {
       printf("  %s                Display help on all parameters\n", cmd_name);
       printf("  %s <param>=<val>...\n", cmd_name);
       printf("  %*s                Add an overlay (with parameters)\n", (int)strlen(cmd_name), "");
       printf("  %s -D [<idx>]     Dry-run (prepare overlay, but don't apply -\n",
	      cmd_name);
       printf("  %*s                save it as dry-run.dtbo)\n", (int)strlen(cmd_name), "");
       printf("  %s -r [<idx>]     Remove an overlay (by index, or the last)\n", cmd_name);
       printf("  %s -R [<idx>]     Remove from an overlay (by index, or all)\n",
	      cmd_name);
       printf("  %s -l             List active overlays/dtparams\n", cmd_name);
       printf("  %s -a             List all overlays/dtparams (marking the active)\n", cmd_name);
       printf("  %s -h             Show this usage message\n", cmd_name);
       printf("  %s -h <param>...  Display help on the listed parameters\n", cmd_name);
    }
    else
    {
       printf("  %s <overlay> [<param>=<val>...]\n", cmd_name);
       printf("  %*s                Add an overlay (with parameters)\n", (int)strlen(cmd_name), "");
       printf("  %s -D [<idx>]     Dry-run (prepare overlay, but don't apply -\n",
	      cmd_name);
       printf("  %*s                save it as dry-run.dtbo)\n", (int)strlen(cmd_name), "");
       printf("  %s -r [<overlay>] Remove an overlay (by name, index or the last)\n", cmd_name);
       printf("  %s -R [<overlay>] Remove from an overlay (by name, index or all)\n",
	      cmd_name);
       printf("  %s -l             List active overlays/params\n", cmd_name);
       printf("  %s -a             List all overlays (marking the active)\n", cmd_name);
       printf("  %s -h             Show this usage message\n", cmd_name);
       printf("  %s -h <overlay>   Display help on an overlay\n", cmd_name);
       printf("  %s -h <overlay> <param>..  Or its parameters\n", cmd_name);
       printf("    where <overlay> is the name of an overlay or 'dtparam' for dtparams\n");
    }
    printf("Options applicable to most variants:\n");
    printf("    -d <dir>    Specify an alternate location for the overlays\n");
    printf("                (defaults to /boot/overlays or /flash/overlays)\n");
    printf("    -v          Verbose operation\n");
    printf("\n");
    printf("Adding or removing overlays and parameters requires root privileges.\n");

    exit(1);
}

获取dts

  • 获取当前运行时系统的dtb：dtc -I fs -O dtb -o base.dtb /proc/device-tree 1>/dev/null 2>&1；
  • 获取设备树：
    • dtc -I dtb -O dts -o basev0.dts base.dtb：basev0.dts；
    • fdtdump base.dtb > basev1.dts；

dtparam i2c_arm=on

  • wget https://github.com/raspberrypi/userland/archive/master.zip
    • unzip master.zip && cd userland-master
    • jar xvf master.zip && cd userland-master
  • sudo apt-get install cmake
  • ./buildme
  • sudo apt-get install ctags
  • ctags -Rn
  • cat ~/.vimrc 
    syntax on
set number

set expandtab
set tabstop=4
set tags=/home/pi/zengjf/dts/userland-master/tags
  • cd ~/zengjf/dts/userland-master/host_applications/linux/apps/dtoverlay
  • sudo dtparam -v i2c_arm=on 
    run_cmd: which dtoverlay-pre >/dev/null 2>&1 && dtoverlay-pre
run_cmd: dtc -I fs -O dtb -o '/tmp/.dtoverlays/base.dtb' /proc/device-tree 1>/dev/null 2>&1
DTOVERLAY[debug]: Found override i2c_arm
DTOVERLAY[debug]:   override i2c_arm: string target 'status'
DTOVERLAY[debug]: delete_node(/__symbols__)
DTOVERLAY[debug]: Wrote 162 bytes to '/tmp/.dtoverlays/1_dtparam.dtbo'
DTOVERLAY[debug]: Wrote 174 bytes to '/sys/kernel/config/device-tree/overlays/1_dtparam/dtbo'
run_cmd: which dtoverlay-post >/dev/null 2>&1 && dtoverlay-post
  • i2c_arm在当前的设备树的状态： 
    __overrides__ {
    [...省略]
    i2c_arm = "", "", "", "!status";
    [...省略]
};
  • 控制台打印输出调试函数：void dtoverlay_debug(const char *fmt, ...);
  • main()
    • dtoverlay_add()
      • DTOVERLAY[debug]: Found override i2c_arm 
        /* Returns a pointer to the override data and (through data_len) its length.
   On error, sets *data_len to be the error code. */
const char *dtoverlay_find_override(DTBLOB_T *dtb, const char *override_name,
                                    int *data_len)
{
   int overrides_off;
   const char *data;
   int len;

   // Find the table of overrides
   overrides_off = fdt_path_offset(dtb->fdt, "/__overrides__");

   if (overrides_off < 0)
   {
      dtoverlay_debug("/__overrides__ node not found");
      *data_len = overrides_off;
      return NULL;
   }

   // Locate the property
   data = fdt_getprop(dtb->fdt, overrides_off, override_name, &len);
   *data_len = len;
   if (data)
      dtoverlay_debug("Found override %s", override_name);
   else
      dtoverlay_debug("/__overrides__ has no %s property", override_name);

   return data;
}

Sense HAT DTS modify

Device Tree Blob Overlay Configuration File System

Linux Kernel configfs

  • drivers/of/Kconfig 
    config OF_CONFIGFS
    bool "Device Tree Overlay ConfigFS interface"
    select CONFIGFS_FS
    select OF_OVERLAY
    help
      Enable a simple user-space driven DT overlay interface.
  • drivers/of/Makefile 
    obj-$(CONFIG_OF_CONFIGFS) += configfs.o
  • drivers/of/Kconfig