linux-kernel - Re: [PATCH v2 1/3] watchdog: imx2_wdg: suspend watchdog in WAIT mode

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Date:   Tue, 25 Oct 2022 07:21:34 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Andrej Picej <andrej.picej@...ik.com>,
        linux-watchdog@...r.kernel.org
Cc:     wim@...ux-watchdog.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, shawnguo@...nel.org,
        s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com,
        linux-imx@....com, Anson.Huang@....com, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] watchdog: imx2_wdg: suspend watchdog in WAIT mode

On 10/25/22 00:25, Andrej Picej wrote:
> Putting device into the "Suspend-To-Idle" mode causes watchdog to
> trigger and reset the board after set watchdog timeout period elapses.
> 

s/reset/resets/

> Introduce new device-tree property "fsl,suspend-in-wait" which suspends
> watchdog in WAIT mode. This is done by setting WDW bit in WCR
> (Watchdog Control Register) Watchdog operation is restored after exiting

'.' after ')' missing ?

> WAIT mode as expected. WAIT mode coresponds with Linux's

s/coresponds/corresponds/

> "Suspend-To-Idle".
> 
> Signed-off-by: Andrej Picej <andrej.picej@...ik.com>
> Reviewed-by: Fabio Estevam <festevam@...il.com>
> ---
> Changes in v2:
>   - validate the property with compatible string, as this functionality
>     is not supported by all devices.
> ---
>   drivers/watchdog/imx2_wdt.c | 37 +++++++++++++++++++++++++++++++++++++
>   1 file changed, 37 insertions(+)
> 
> diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
> index d0c5d47ddede..dd9866c6f1e5 100644
> --- a/drivers/watchdog/imx2_wdt.c
> +++ b/drivers/watchdog/imx2_wdt.c
> @@ -35,6 +35,7 @@
>   
>   #define IMX2_WDT_WCR		0x00		/* Control Register */
>   #define IMX2_WDT_WCR_WT		(0xFF << 8)	/* -> Watchdog Timeout Field */
> +#define IMX2_WDT_WCR_WDW	BIT(7)		/* -> Watchdog disable for WAIT */
>   #define IMX2_WDT_WCR_WDA	BIT(5)		/* -> External Reset WDOG_B */
>   #define IMX2_WDT_WCR_SRS	BIT(4)		/* -> Software Reset Signal */
>   #define IMX2_WDT_WCR_WRE	BIT(3)		/* -> WDOG Reset Enable */
> @@ -67,6 +68,27 @@ struct imx2_wdt_device {
>   	bool ext_reset;
>   	bool clk_is_on;
>   	bool no_ping;
> +	bool sleep_wait;
> +};
> +
> +static const char * const wdw_boards[] __initconst = {
> +	"fsl,imx25-wdt",
> +	"fsl,imx35-wdt",
> +	"fsl,imx50-wdt",
> +	"fsl,imx51-wdt",
> +	"fsl,imx53-wdt",
> +	"fsl,imx6q-wdt",
> +	"fsl,imx6sl-wdt",
> +	"fsl,imx6sll-wdt",
> +	"fsl,imx6sx-wdt",
> +	"fsl,imx6ul-wdt",
> +	"fsl,imx7d-wdt",
> +	"fsl,imx8mm-wdt",
> +	"fsl,imx8mn-wdt",
> +	"fsl,imx8mp-wdt",
> +	"fsl,imx8mq-wdt",
> +	"fsl,vf610-wdt",
> +	NULL
>   };
>   
>   static bool nowayout = WATCHDOG_NOWAYOUT;
> @@ -129,6 +151,9 @@ static inline void imx2_wdt_setup(struct watchdog_device *wdog)
>   
>   	/* Suspend timer in low power mode, write once-only */
>   	val |= IMX2_WDT_WCR_WDZST;
> +	/* Suspend timer in low power WAIT mode, write once-only */
> +	if (wdev->sleep_wait)
> +		val |= IMX2_WDT_WCR_WDW;
>   	/* Strip the old watchdog Time-Out value */
>   	val &= ~IMX2_WDT_WCR_WT;
>   	/* Generate internal chip-level reset if WDOG times out */
> @@ -313,6 +338,18 @@ static int __init imx2_wdt_probe(struct platform_device *pdev)
>   
>   	wdev->ext_reset = of_property_read_bool(dev->of_node,
>   						"fsl,ext-reset-output");
> +
> +	if (of_property_read_bool(dev->of_node, "fsl,suspend-in-wait"))
> +		if (of_device_compatible_match(dev->of_node, wdw_boards))
> +			wdev->sleep_wait = 1;

Since sleep_wait is bool:
			wdev->sleep_wait = true;

> +		else {
> +			dev_warn(dev, "Warning: Suspending watchdog during " \
> +				"WAIT mode is not supported for this device.\n");

Do not split strings. "Warning:" is redundant. Please handle the error first.

> +			wdev->sleep_wait = 0;

Unnecessary; false by default. Also, this should fail and return -EINVAL.
Devicetree files should be correct, and warning messages tend to be ignored.

> +		}

All branches of if/else need to wither use {} or no {}.

> +	else
> +		wdev->sleep_wait = 0;
> +
Unnecessary.

I would suggest to replace the above code with something like

	if (of_property_read_bool(dev->of_node, "fsl,suspend-in-wait")) {
		if (!of_device_compatible_match(dev->of_node, wdw_boards)) {
			dev_err(dev, "Suspending watchdog in WAIT mode is not supported for this device\n");
			return -EINVAL;
		}
		wdev->sleep_wait = true;
	}

>   	/*
>   	 * The i.MX7D doesn't support low power mode, so we need to ping the watchdog
>   	 * during suspend.

I still wonder how that interacts with fsl,suspend-in-wait, but since we have a
property for that we can leave that for someone else to find out. Maybe add a
comment explaining that interaction with "fsl,suspend-in-wait" is unknown.

Thanks,
Guenter