作者：付汉杰 hankf@amd.com，来源：博客园
U-Boot 2020.2 启动问题
最近有客户反馈，U-Boot 2020.2 启动有问题。 SD卡里有BOOT.BIN, image.ub等文件，也不能正常启动。
下面是常见的启动信息。 U-Boot报告多个错误，最主要的错误是“Wrong image format for "source" command”。
U-Boot 2020.01 (Nov 20 2020 - 19:24:17 +0000)
Model: ZynqMP ZCU106 RevA
Board: Xilinx ZynqMP
DRAM: 4 GiB
PMUFW: v1.1
EL Level: EL2
Chip ID: zu7ev
NAND: 0 MiB
MMC: mmc@ff170000: 0
In: serial@ff000000
Out: serial@ff000000
Err: serial@ff000000
Bootmode: LVL_SHFT_SD_MODE1
Reset reason: EXTERNAL
Net:
ZYNQ GEM: ff0e0000, mdio bus ff0e0000, phyaddr 12, interface rgmii-id
Warning: ethernet@ff0e0000 using MAC address from ROM
eth0: ethernet@ff0e0000
Hit any key to stop autoboot: 0
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:1...
JTAG: Trying to boot script at 0x20000000
## Executing script at 20000000
Wrong image format for "source" command
JTAG: SCRIPT FAILED: continuing...
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:1...
MMC Device 1 not found
no mmc device at slot 1
SF: Detected n25q512a with page size 512 Bytes, erase size 128 KiB, total 128 MiB
device 0 offset 0x3e80000, size 0x80000
SF: 524288 bytes @ 0x3e80000 Read: OK
QSPI: Trying to boot script at 0x20000000
## Executing script at 20000000
Wrong image format for "source" command
QSPI: SCRIPT FAILED: continuing...
no devices available
NAND: SCRIPT FAILED: continuing...
starting USB...
Bus dwc3@fe200000: usb maximum-speed not found
Register 2000440 NbrPorts 2
Starting the controller
USB XHCI 1.00
scanning bus dwc3@fe200000 for devices... 1 USB Device(s) found
scanning usb for storage devices... 0 Storage Device(s) found
Device 0: unknown device
Device 1: unknown device
scanning bus for devices...
SATA link 0 timeout.
SATA link 1 timeout.
AHCI 0001.0301 32 slots 2 ports 6 Gbps 0x3 impl SATA mode
flags: 64bit ncq pm clo only pmp fbss pio slum part ccc apst
Device 0: unknown device
BOOTP broadcast 1
DHCP client bound to address 10.164.16.148 (166 ms)
*** ERROR: `serverip' not set
Cannot autoload with TFTPGET
missing environment variable: pxeuuid
Retrieving file: pxelinux.cfg/01-00-0a-35-04-d2-38
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/0AA41094
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/0AA4109
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/0AA410
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/0AA41
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/0AA4
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/0AA
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/0A
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/0
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/default-arm-zynqmp-zynqmp
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/default-arm-zynqmp
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/default-arm
*** ERROR: `serverip' not set
Retrieving file: pxelinux.cfg/default
*** ERROR: `serverip' not set
Config file not found
BOOTP broadcast 1
DHCP client bound to address 10.164.16.148 (164 ms)
*** ERROR: `serverip' not set
Cannot autoload with TFTPGET
BOOTP broadcast 1
DHCP client bound to address 10.164.16.148 (176 ms)
*** ERROR: `serverip' not set
Cannot autoload with TFTPGET
问题原因和解决办法
上述问题是在启动设备里没有文件“boot.scr”导致的。 如果在SD卡里，提供文件 boot.scr，就能正常启动。
U-Boot 2020.01 (Nov 20 2020 - 19:24:17 +0000)
Model: ZynqMP ZCU106 RevA
Board: Xilinx ZynqMP
DRAM: 4 GiB
PMUFW: v1.1
EL Level: EL2
Chip ID: zu7ev
NAND: 0 MiB
MMC: mmc@ff170000: 0
In: serial@ff000000
Out: serial@ff000000
Err: serial@ff000000
Bootmode: LVL_SHFT_SD_MODE1
Reset reason: EXTERNAL
Net:
ZYNQ GEM: ff0e0000, mdio bus ff0e0000, phyaddr 12, interface rgmii-id
Warning: ethernet@ff0e0000 using MAC address from ROM
eth0: ethernet@ff0e0000
Hit any key to stop autoboot: 0
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:1...
Found U-Boot script /boot.scr
1718 bytes read in 21 ms (79.1 KiB/s)
## Executing script at 20000000
124511736 bytes read in 8225 ms (14.4 MiB/s)
## Loading kernel from FIT Image at 10000000 ...
Using 'conf@system-top.dtb' configuration
Trying 'kernel@1' kernel subimage
......
U-Boot 2020.2 启动流程分析
U-Boot 文档
U-Boot为了支持各种Linux发行版，增加通用性，增加了启动时的Script的功能。 详细信息可以参考文档文件doc/develop/distro.rst和Generic Distro Configuration Concept 。
U-Boot对Script是逐步完善的。软件代码文件“include/config_distro_bootcmd.h”在2015.01就已经存在。文档文件“doc/develop/distro.rst”在2022.01里加入。
业界对Script功能也逐步接受，目前很多芯片都都已经默认使能，比如AMD的MPSoC的U-Boot。
如果不想使用Script功能，可以禁止选项CONFIG_DISTRO_DEFAULTS。
U-Boot启动命令
没有人工参与的自动启动，或者直接执行命令“boot”， U-Boot启动命令都是“bootcmd”。
超时启动代码
下面是没有人工参与，超时启动时选择启动命令的代码。
const char *bootdelay_process(void)
{
char *s;
int bootdelay;
bootcount_inc();
s = env_get("bootdelay");
bootdelay = s ? (int)simple_strtol(s, NULL, 10) : CONFIG_BOOTDELAY;
if (IS_ENABLED(CONFIG_OF_CONTROL)) {
bootdelay = ofnode_conf_read_int("bootdelay", bootdelay);
}
debug("### main_loop entered: bootdelay=%d\n\n", bootdelay);
if (IS_ENABLED(CONFIG_AUTOBOOT_MENU_SHOW)) {
bootdelay = menu_show(bootdelay);
}
bootretry_init_cmd_timeout();
#ifdef CONFIG_POST
if (gd->flags & GD_FLG_POSTFAIL) {
s = env_get("failbootcmd");
} else
#endif /* CONFIG_POST */
if (bootcount_error()) {
s = env_get("altbootcmd");
} else {
s = env_get("bootcmd");
}
if (IS_ENABLED(CONFIG_OF_CONTROL)) {
process_fdt_options(gd->fdt_blob);
}
stored_bootdelay = bootdelay;
return s;
}
命令“boot”的启动代码
下面是直接执行命令“boot”选择启动命令的代码。
int do_bootd(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
{
return run_command(env_get("bootcmd"), flag);
}
U_BOOT_CMD(
boot, 1, 1, do_bootd,
"boot default, i.e., run 'bootcmd'",
""
);
/* keep old command name "bootd" for backward compatibility */
U_BOOT_CMD(
bootd, 1, 1, do_bootd,
"boot default, i.e., run 'bootcmd'",
""
);
命令distro_bootcmd
启动命令“bootcmd”通常是“run distro_bootcmd”。 它在“boot\Kconfig”中定义，能在配置U-Boot时更改。
config BOOTCOMMAND
string "bootcmd value"
depends on USE_BOOTCOMMAND && !USE_DEFAULT_ENV_FILE
default "run distro_bootcmd" if DISTRO_DEFAULTS
help
This is the string of commands that will be used as bootcmd and if
AUTOBOOT is set, automatically run.
“distro_bootcmd”的定义在include\Config_distro_bootcmd.h里。
"distro_bootcmd=" BOOTENV_SET_SCSI_NEED_INIT \
BOOTENV_SET_NVME_NEED_INIT \
BOOTENV_SET_IDE_NEED_INIT \
BOOTENV_SET_VIRTIO_NEED_INIT \
"for target in ${boot_targets}; do " \
"run bootcmd_${target}; " \
"done\0"
在U-Boot启动时，使用键盘进入U-Boot的命令行界面，使用命令“printenv”也可以查看真实的“distro_bootcmd”。 与“distro_bootcmd”相关的环境变量如下：
boot_a_script=load ${devtype} ${devnum}:${distro_bootpart} ${scriptaddr} ${prefix}${script}; source ${scriptaddr}
boot_scripts=boot.scr.uimg boot.scr
boot_targets=mmc0 jtag mmc0 mmc1 qspi0 nand0 usb0 usb1 scsi0 pxe dhcp
bootcmd=run distro_bootcmd
bootcmd_jtag=echo JTAG: Trying to boot script at ${scriptaddr} && source ${scriptaddr}; echo JTAG: SCRIPT FAILED: continuing...;
bootcmd_mmc0=devnum=0; run mmc_boot
bootcmd_mmc1=devnum=1; run mmc_boot
bootcmd_qspi0=sf probe 0 0 0 && sf read $scriptaddr $script_offset_f $script_size_f && echo QSPI: Trying to boot script at ${scriptaddr} && source ${scriptaddr}; echo QSPI: SCRIPT FAILED: continuing...;
distro_bootcmd=scsi_need_init=; for target in ${boot_targets}; do run bootcmd_${target}; done
mmc_boot=if mmc dev ${devnum}; then devtype=mmc; run scan_dev_for_boot_part; fi
modeboot=sdboot
scan_dev_for_boot=echo Scanning ${devtype} ${devnum}:${distro_bootpart}...; for prefix in ${boot_prefixes}; do run scan_dev_for_extlinux; run scan_dev_for_scripts; done;run scan_dev_for_efi;
scan_dev_for_boot_part=part list ${devtype} ${devnum} -bootable devplist; env exists devplist || setenv devplist 1; for distro_bootpart in ${devplist}; do if fstype ${devtype} ${devnum}:${distro_bootpart} bootfstype; then run scan_dev_for_boot; fi; done; setenv devplist
scan_dev_for_scripts=for script in ${boot_scripts}; do if test -e ${devtype} ${devnum}:${distro_bootpart} ${prefix}${script}; then echo Found U-Boot script ${prefix}${script}; run boot_a_script; echo SCRIPT FAILED: continuing...; fi; done
script_offset_f=3e80000
script_size_f=0x80000
scriptaddr=0x20000000
可以看到，U-Boot会依次执行bootcmd_mmc0， bootcmd_jtag， bootcmd_mmc0， bootcmd_mmc1， bootcmd_qspi0，与上述的错误信息中的设备启动顺序一致。也说明U-Boot能从各种设备启动Linux。
另外bootcmd_mmc0会依次调用mmc_boot， scan_dev_for_boot_part， scan_dev_for_boot， scan_dev_for_scripts。最后scan_dev_for_scripts检查U-Boot script，也就是前述的“boot.scr”。如果发现，就会输出“Found U-Boot script”，并执行“boot_a_script”。 对于ZCU106单板，mmc0就是SD卡。 如果没有前述的“boot.scr”，就会尝试后续的启动设备。
因此，默认的U-Boot启动过程中，需要“boot.scr”。如果不想使用“boot.scr”，可以在配置U-Boot时禁止选项CONFIG_DISTRO_DEFAULTS，或者把替换启动命令“bootcmd”成直接从某个固定设备启动Linux的命令。当然，也可以在运行时，直接修改U-Boot环境变量中的命令“bootcmd”，让它直接从某个固定设备启动Linux。
