Re: [Buildroot] RaspberryPi U-Boot watchdog

[Fiona Klute via buildroot <buildroot@buildroot.org>]

Hi José!

Am 24.07.24 um 12:16 schrieb José Mendes:
> Hi all,
>
> I'm trying to build a system with redundant rootfs partitions for a
> Raspberry Pi 4 with U-Boot.
>
> I'm trying to test the recovery of this system but I can't seem to get the
> raspberry pi to reset after a kernel panic on a non-working rootfs.
>
> To provoke this kernel panic I am simply deleting all the files in the
> particular rootfs. The system seems to just hang there after the panic:
>
> .....
> [    3.374273] Kernel panic - not syncing: No working init found.  Try
> passing init= option to kernel. See Linux
> Documentation/admin-guide/init.rst for guidance.
> [    3.388444] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 6.1.61-v8 #2
> [    3.394627] Hardware name: Raspberry Pi 4 Model B Rev 1.5 (DT)
> [    3.400456] Call trace:
> [    3.402897]  dump_backtrace.part.0+0xe8/0x100
> [    3.407264]  show_stack+0x20/0x30
> [    3.410579]  dump_stack_lvl+0x88/0xb4
> [    3.414246]  dump_stack+0x18/0x34
> [    3.417561]  panic+0x1a0/0x370
> [    3.420618]  kernel_init+0x138/0x140
> [    3.424197]  ret_from_fork+0x10/0x20
> [    3.427776] SMP: stopping secondary CPUs
> [    3.431701] Kernel Offset: 0x1353c00000 from 0xffffffc008000000
> [    3.437617] PHYS_OFFSET: 0x0
> [    3.440492] CPU features: 0x80000,2013c080,0000421b
> [    3.445368] Memory Limit: none
> [    3.448423] ---[ end Kernel panic - not syncing: No working init found.
> Try passing init= option to kernel. See Linux
> Documentation/admin-guide/init.rst for guidance. ]---
>
> What I've tried:
> - From `Target packages`: watchdog, watchdogd
> - Busybox watchdog
> - From linux-menuconfig > device drivers > watchdog
> - From uboot-menuconfig > device drivers > watchdog
>
> None of these seem to be working for me.

The config options in menuconfig (both for U-Boot and Linux) only enable
the drivers to support the watchdog. The kernel can handle watchdogs
internally (see CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED and
CONFIG_WATCHDOG_OPEN_TIMEOUT in the kernel config), but generally you
want that only as a transitory thing during boot before a watchdog
service (whether watchdogd or Busybox watchdog) takes over.

If you want the watchdog to reset no matter how broken the kernel or
userspace may be, enable the watchdog in U-Boot *before* starting the
kernel using the "wdt" command:
https://docs.u-boot.org/en/latest/usage/cmd/wdt.html

Excerpt from my boot.scr that configures the watchdog of an RPi CM4 (so,
the device may be different for you, and you need the matching driver
enabled in the U-Boot config) to expect a pet every 15 seconds:

wdt dev watchdog@7e100000
wdt start 15000

Of course the system then needs to boot up far enough to handle the
watchdog before that time is over.

Best regards,
Fiona

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