Re: [PATCH v5 6/8] watchdog: rzv2h: Add syscon support for WDTDCR

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Watchdog restart handler may deadlock during system panic because it executes a locked regmap operation on a syscon regmap.
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commit a3a7e98fdd4da0cb2994accaf697498b31aba4d4
Author: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>

watchdog: rzv2h: Add syscon support for WDTDCR

This commit introduces syscon regmap support for the WDTDCR (WDT Debug Control
Register) on RZ/T2H and RZ/N2H SoCs. It retrieves the SYSC regmap using the
"renesas,sysc" property and derives the WDTDCR offset from the watchdog
instance index, while preserving MMIO compatibility when the property is absent.

> diff --git a/drivers/watchdog/rzv2h_wdt.c b/drivers/watchdog/rzv2h_wdt.c
> index 550112446db49..9dee410ab7f31 100644
> --- a/drivers/watchdog/rzv2h_wdt.c
> +++ b/drivers/watchdog/rzv2h_wdt.c

[ ... ]

>  static inline int rzt2h_wdt_wdtdcr_count_start_nolock(struct rzv2h_wdt_priv *priv)
>  {
> -	return regmap_clear_bits(priv->wdtdcr_regmap, WDTDCR, WDTDCR_WDTSTOPCTRL);
> +	struct rzv2h_sysc_wdtdcr *sysc = &priv->sysc;
> +
> +	return regmap_clear_bits(sysc->regmap, sysc->offset, WDTDCR_WDTSTOPCTRL);
>  }

[Severity: High]
Does this introduce a deadlock risk during a system panic?

The watchdog restart handler, rzv2h_wdt_restart(), expects an unlocked
execution path to avoid deadlocks and specifically calls this nolock variant:

	if (priv->of_data->wdtdcr) {
		/*
		 * Best effort, ignore return value and use the unlocked
		 * variant of the function to avoid potential deadlocks.
		 */
		rzt2h_wdt_wdtdcr_count_start_nolock(priv);
	}

Previously, the driver used a dedicated MMIO regmap with
.disable_locking = true. Now that sysc->regmap can be a syscon regmap,
which is shared and uses internal spinlocks, regmap_clear_bits() will attempt
to acquire the syscon lock.

If the system panics while another CPU holds this shared syscon spinlock,
will attempting to acquire it here cause the panic handler to hang instead of
resetting the system?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260911111731.3404308-1-prabhakar.mahadev-lad.rj@bp.renesas.com?part=6