That's a software watchdog. The comment you're replying to is talking about hardware watchdogs.

Yes, but those are done in software

There's generally at least one watchdog device available in most PCs delivered in last decade, but it's not always utilized. Essentially at one point an intel southbridge integrated a basic watchdog on all models, and it started to just... be included.

So these days you can find a variation on the TCO timer watchdog in most PCs, even if the exact implementation varies so we now have a bunch of drivers for the different variants.

Linux doesn't see one on my Ryzen 5600X desktop at least. My Intel Skylake Thinkpad does seem to have two though (iTCO as well as INT3F0D, not sure what that is, but if I interpret the files under /sys correctly it belongs to the LPC/eSPI controller PCIe device, while the TCO watchdog is found under the SMBus PCIe device).

In both cases they do have software watchdogs (NMI based) which relies on a hardware timer triggering an NMI in the kernel. But that relies on the NMI handler still working, which is not as good as a real HW watchdog.

Apparently it depends to a little bit on how the motherboard is designed, theoretically SP5100 watchdog which is part of the CPU logic in recent ryzens, apparently, is supposed to be enabled if the motherboard is designed with IPMI in mind.

For whatever reason, it's enabled on my laptop despite it obviously not having IPMI support :)

mac’s too?

“All CPUs” would probably be 99.9999% accurate. It’s just one of those fundamental functions you want in a processor. Whether it’s exposed in the OS is a different matter.

AMD doesn't have it. I just confirmed by grepping through dmesg and journalctl -b, the only time it appears is due to UPS driver notifications (unrelated).

Cortex-A includes a watchdog so yeah.