Re: [PATCH v4] watchdog: Add ARM TWD (MPCore private) watchdog driver

[Guenter Roeck <linux@roeck-us.net>]

On 11/14/26 06:11, Fil Dunsky via B4 Relay wrote:
> From: Fil Dunsky <filipp.dunsky@gmail.com>
> 
> ARM11 MPCore, Cortex-A5 and Cortex-A9 MPCore systems have a watchdog
> next to the local timer of every CPU, banked at the same address. The
> binding "arm,cortex-a9-twd-wdt" exists, but there has been no driver
> since mpcore_wdt was removed in v3.11, among other reasons because it
> only ever programmed the CPU that ran the ioctl.
> 
> Program, ping and stop the watchdogs of all online CPUs together with
> on_each_cpu(), and use a CPU hotplug state to arm the watchdog of a CPU
> coming online while the device is active and to stop it on a CPU going
> offline, which could not ping it any more. The watchdog is used in reset
> mode only, its interrupt is not needed.
> 

Watchdog drivers are supposed to watch the system as a whole, not on a
per-CPU level. This patch goes way beyond the scope of a system watchdog
driver. Per-CPU watchdogs are handled in kernel/watchdog.c. I do not think
it is a good idea to overlay that with a second per-CPU watchdog mechanism.

Guenter