Re: [PATCH v2 3/8] watchdog: starfive-wdt: Avoid unclocked register access in remove and PM paths

[Tzung-Bi Shih <tzungbi@kernel.org>]

On Thu, Nov 05, 2026 at 11:05:24AM -0800, Guenter Roeck wrote:
> When runtime PM is enabled and the watchdog is inactive, the device enters
> runtime suspend and starfive_wdt_runtime_suspend() disables core_clk and
> apb_clk.
> 
> However, starfive_wdt_remove(), starfive_wdt_shutdown(),
> starfive_wdt_suspend(), and starfive_wdt_resume() unconditionally read and
> write watchdog MMIO registers without checking whether the watchdog is
> running or clocks are enabled, causing a bus fault when the device is
> runtime-suspended:
> 
> - In starfive_wdt_remove(), starfive_wdt_stop() is called before
>   watchdog_unregister_device() while clocks may be gated off. Unregister
>   the watchdog device first (which stops an active watchdog via
>   watchdog_stop_on_unregister while its runtime PM reference keeps clocks
>   enabled), and only call starfive_wdt_stop() if watchdog_hw_running() is
>   still set.
> - In starfive_wdt_pm_stop(), check pm_runtime_enabled() and ignore
>   non-zero idle return codes from pm_runtime_put_sync() so watchdog_stop()
>   does not falsely treat a stopped watchdog as still running.
> - Remove the redundant starfive_wdt_shutdown() callback. Because
>   starfive_wdt_probe() already sets watchdog_stop_on_reboot(),
>   watchdog_reboot_notifier() stops a running watchdog on reboot, halt, or
>   power-off (while respecting the watchdog.stop_on_reboot parameter)
>   before device_shutdown() runs; calling starfive_wdt_pm_stop() again in
>   .shutdown causes unclocked MMIO when suspended and an unbalanced
>   pm_runtime_put_sync() when inactive or already stopped.
> - In starfive_wdt_suspend() and starfive_wdt_resume(), only save/stop and
>   restore/restart the hardware watchdog when watchdog_hw_running() is set
>   (in which case an active runtime PM reference ensures clocks are enabled
>   before suspend and re-enabled by pm_runtime_force_resume()).
> 
> Fixes: db728ea9c7be ("drivers: watchdog: Add StarFive Watchdog driver")
> Cc: Xingyu Wu <xingyu.wu@starfivetech.com>
> Cc: Ziv Xu <ziv.xu@starfivetech.com>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>