Re: [PATCH 1/3] watchdog: realtek-otto: Change to use regmap API

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Deadlock risk in the atomic restart handler due to regmap's internal spinlock.
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commit a520c8e2203154ba331a6ae28f00daec074e62ee
Author: Rustam Adilov <adilov@disroot.org>

watchdog: realtek-otto: Change to use regmap API

This commit converts the realtek-otto watchdog driver to use the regmap API
instead of direct mmio accesses. It replaces direct read/modify/write
sequences with regmap functions and selects REGMAP_MMIO.

> diff --git a/drivers/watchdog/realtek_otto_wdt.c b/drivers/watchdog/realtek_otto_wdt.c
> index 2c30ddd574c59..e5e9cb480f4f9 100644
> --- a/drivers/watchdog/realtek_otto_wdt.c
> +++ b/drivers/watchdog/realtek_otto_wdt.c
[ ... ]
> @@ -199,7 +189,7 @@ static int otto_wdt_restart(struct watchdog_device *wdev, unsigned long reboot_m
>  
>  	/* Configure for shortest timeout and wait for reset to occur */
>  	v = FIELD_PREP(OTTO_WDT_CTRL_RST_MODE, reset_mode) | OTTO_WDT_CTRL_ENABLE;
> -	iowrite32(v, ctrl->base + OTTO_WDT_REG_CTRL);
> +	regmap_write(ctrl->regmap, OTTO_WDT_REG_CTRL, v);

Could this regmap_write() cause a deadlock during system restart?

The restart handler is often called during system shutdown or kernel panic
in an atomic context with local interrupts disabled. Since
devm_regmap_init_mmio() configures the regmap to use a spinlock by default,
if a panic occurs while another cpu holds the regmap lock (e.g., during
a ping or timeout update) and that cpu is halted by smp_send_stop(), this
regmap_write() could spin endlessly and prevent the system from rebooting.

Additionally, on preempt-rt kernels, the regmap spinlock becomes a sleepable
rt_mutex, which could cause a sleeping in atomic context bug when acquired
with interrupts disabled.

>  	mdelay(3 * otto_wdt_tick_ms(ctrl, 0));
>

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Sashiko AI review · https://sashiko.dev/#/patchset/20260509163101.722793-1-adilov@disroot.org?part=1