Re: [PATCH v6 4/8] watchdog: rzv2h: Propagate WDTDCR access errors

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

On Wed, Sep 23, 2026 at 11:40:50AM +0100, Prabhakar wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> 
> The WDTDCR helpers access the register directly using readl()/writel() and
> therefore cannot report failures to their callers. WDTDCR is located in a
> shared syscon region and will be accessed through regmap in a subsequent
> change, where register accesses can fail.
> 
> Make rzt2h_wdt_wdtdcr_count_start() and rzt2h_wdt_wdtdcr_count_stop()
> return an error so their callers can propagate failures.
> 
> Handle these errors in the watchdog start and stop paths and unwind the
> resources acquired before the WDTDCR access, restoring the reset state.
> 
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> ---
> v5->v6:
> - No change
> 
> v4->v5:
> - Dropped checking rzt2h_wdt_wdtdcr_count_start() return value in
>   restart path.
> 
> v2->v3:
> - New patch, split from v2 patch #1 to make thing easier to review.
> ---
>  drivers/watchdog/rzv2h_wdt.c | 35 ++++++++++++++++++++++++++---------
>  1 file changed, 26 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/watchdog/rzv2h_wdt.c b/drivers/watchdog/rzv2h_wdt.c
> index 9774fe8e441e..a65e5d6c48ad 100644
> --- a/drivers/watchdog/rzv2h_wdt.c
> +++ b/drivers/watchdog/rzv2h_wdt.c
> @@ -87,18 +87,22 @@ static int rzv2h_wdt_ping(struct watchdog_device *wdev)
>  	return 0;
>  }
>  
> -static void rzt2h_wdt_wdtdcr_count_stop(struct rzv2h_wdt_priv *priv)
> +static int rzt2h_wdt_wdtdcr_count_stop(struct rzv2h_wdt_priv *priv)
>  {
>  	u32 reg = readl(priv->wdtdcr + WDTDCR);
>  
>  	writel(reg | WDTDCR_WDTSTOPCTRL, priv->wdtdcr + WDTDCR);
> +
> +	return 0;
>  }
>  
> -static void rzt2h_wdt_wdtdcr_count_start(struct rzv2h_wdt_priv *priv)
> +static int rzt2h_wdt_wdtdcr_count_start(struct rzv2h_wdt_priv *priv)
>  {
>  	u32 reg = readl(priv->wdtdcr + WDTDCR);
>  
>  	writel(reg & ~WDTDCR_WDTSTOPCTRL, priv->wdtdcr + WDTDCR);
> +
> +	return 0;
>  }
>  
>  static void rzv2h_wdt_setup(struct watchdog_device *wdev, u16 wdtcr)
> @@ -148,8 +152,14 @@ static int rzv2h_wdt_start(struct watchdog_device *wdev)
>  	rzv2h_wdt_setup(wdev, of_data->cks_max | WDTCR_RPSS_100 |
>  			WDTCR_RPES_0 | of_data->tops);
>  
> -	if (priv->of_data->wdtdcr)
> -		rzt2h_wdt_wdtdcr_count_start(priv);
> +	if (priv->of_data->wdtdcr) {
> +		ret = rzt2h_wdt_wdtdcr_count_start(priv);
> +		if (ret) {
> +			reset_control_assert(priv->rstc);

It seems to me this does way more than handling the error:
it puts the module into reset and calls pm_runtime_put()
on the parent. This is a substantial functional change
that is not explained.

> +			pm_runtime_put(wdev->parent);
> +			return ret;
> +		}
> +	}
>  
>  	/*
>  	 * Down counting starts after writing the sequence 00h -> FFh to the
> @@ -169,8 +179,13 @@ static int rzv2h_wdt_stop(struct watchdog_device *wdev)
>  	if (ret)
>  		return ret;
>  
> -	if (priv->of_data->wdtdcr)
> -		rzt2h_wdt_wdtdcr_count_stop(priv);
> +	if (priv->of_data->wdtdcr) {
> +		ret = rzt2h_wdt_wdtdcr_count_stop(priv);
> +		if (ret) {
> +			reset_control_deassert(priv->rstc);

Same here, and the logic behind taking the module out of reset
in the stop function and putting it into reset in the start function
isn't obvious to me.

Frankly, I think it would be much better and risk fewer problems
to just ignore the theoretic errors from the regmap functions.

> +			return ret;
> +		}
> +	}
>  
>  	pm_runtime_put_sync(wdev->parent);
>  
> @@ -219,8 +234,10 @@ static int rzv2h_wdt_restart(struct watchdog_device *wdev,
>  	rzv2h_wdt_setup(wdev, priv->of_data->cks_min | WDTCR_RPSS_25 |
>  			WDTCR_RPES_75 | WDTCR_TOPS_1024);
>  
> -	if (priv->of_data->wdtdcr)
> +	if (priv->of_data->wdtdcr) {
> +		/* best effort, ignore ret */
>  		rzt2h_wdt_wdtdcr_count_start(priv);
> +	}
>  
>  	rzv2h_wdt_ping(wdev);
>  
> @@ -251,11 +268,11 @@ static int rzt2h_wdt_wdtdcr_init(struct platform_device *pdev,
>  	if (ret)
>  		return ret;
>  
> -	rzt2h_wdt_wdtdcr_count_stop(priv);
> +	ret = rzt2h_wdt_wdtdcr_count_stop(priv);
>  
>  	pm_runtime_put_sync(&pdev->dev);
>  
> -	return 0;
> +	return ret;
>  }
>  
>  static int rzv2h_wdt_probe(struct platform_device *pdev)
> -- 
> 2.55.0
>