Re: [PATCH V3] watchdog: mtk: support pre-timeout when the bark irq is available

[Guenter Roeck]

On 4/14/21 4:48 AM, Wang Qing wrote:
> Use the bark interrupt as the pretimeout notifier if available.
> 
> By default, the pretimeout notification shall occur one second earlier
> than the timeout.
> 
> V2:
> - panic() by default if WATCHDOG_PRETIMEOUT_GOV is not enabled.
> 
> V3:
> - Modify the pretimeout behavior, manually reset after the pretimeout
> - is processed and wait until timeout.
> 
> Signed-off-by: Wang Qing <wangqing@xxxxxxxx>
> ---
>  drivers/watchdog/mtk_wdt.c | 62 ++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 57 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/watchdog/mtk_wdt.c b/drivers/watchdog/mtk_wdt.c
> index 97ca993..7bef1e3
> --- a/drivers/watchdog/mtk_wdt.c
> +++ b/drivers/watchdog/mtk_wdt.c
> @@ -25,6 +25,7 @@
>  #include <linux/reset-controller.h>
>  #include <linux/types.h>
>  #include <linux/watchdog.h>
> +#include <linux/interrupt.h>
>  
>  #define WDT_MAX_TIMEOUT		31
>  #define WDT_MIN_TIMEOUT		1
> @@ -234,18 +235,46 @@ static int mtk_wdt_start(struct watchdog_device *wdt_dev)
>  	void __iomem *wdt_base = mtk_wdt->wdt_base;
>  	int ret;
>  
> -	ret = mtk_wdt_set_timeout(wdt_dev, wdt_dev->timeout);
> +	ret = mtk_wdt_set_timeout(wdt_dev, wdt_dev->timeout - wdt_dev->pretimeout);
>  	if (ret < 0)
>  		return ret;
>  
>  	reg = ioread32(wdt_base + WDT_MODE);
> -	reg &= ~(WDT_MODE_IRQ_EN | WDT_MODE_DUAL_EN);
> +	reg &= ~WDT_MODE_IRQ_EN;
> +	if (wdt_dev->pretimeout)
> +		reg |= WDT_MODE_IRQ_EN;
> +	else
> +		reg &= ~WDT_MODE_IRQ_EN;
>  	reg |= (WDT_MODE_EN | WDT_MODE_KEY);
>  	iowrite32(reg, wdt_base + WDT_MODE);
>  
>  	return 0;
>  }
>  
> +static int mtk_wdt_set_pretimeout(struct watchdog_device *wdd,
> +				   unsigned int timeout)
> +{
> +	wdd->pretimeout = timeout;
> +	return mtk_wdt_start(wdd);

The watchdog is not necessarily active here.

> +}
> +
> +static irqreturn_t mtk_wdt_isr(int irq, void *arg)
> +{
> +	struct watchdog_device *wdd = arg;
> +	struct mtk_wdt_dev *mtk_wdt = watchdog_get_drvdata(wdd);
> +	void __iomem *wdt_base = mtk_wdt->wdt_base;
> +
> +	watchdog_notify_pretimeout(wdd);
> +	/*
> +	 * Guaranteed to be reset when the timeout
> +	 * expires under any situations
> +	 */
> +	mdelay(1000*wdd->pretimeout);

That is not how this is supposed to work. The idea with a pretimeout is that the
real watchdog reset will happen under all circumstances, and that executing
the pretimeout (and changing some hardware registers) is not a prerequisite
for the real timeout to happen. After all, the system could be stuck hard, with
interrupts disabled.

On top of that, just sleeping here while waiting for the real timeout and
then resetting the system isn't the idea either. On a single core system this
will just hang. On a multi-core system, who knows if userspace managed to ping
the watchdog in the meantime.

Unless there is a means to trigger the watchdog twice, without intervention,
the first time generating an interrupt and the second time resetting the system,
there is no way for this to work. I don't see how this chip really supports
pretimeout. It seems that it supports either a hard reset or generating an
interrupt on watchdog timeout, and there is only a single timeout.

If you have a use case for generating an interrupt and resetting the system via
software (ie panic) _instead_ of having it generate a hard reset, please feel
free to submit a patch along that line, together with a description of its use
case.

Thanks,
Guenter

> +	writel(WDT_SWRST_KEY, wdt_base + WDT_SWRST);
> +
> +	return IRQ_HANDLED;
> +}
> +
>  static const struct watchdog_info mtk_wdt_info = {
>  	.identity	= DRV_NAME,
>  	.options	= WDIOF_SETTIMEOUT |
> @@ -253,12 +282,21 @@ static const struct watchdog_info mtk_wdt_info = {
>  			  WDIOF_MAGICCLOSE,
>  };
>  
> +static const struct watchdog_info mtk_wdt_pt_info = {
> +	.identity	= DRV_NAME,
> +	.options	= WDIOF_SETTIMEOUT |
> +			  WDIOF_PRETIMEOUT |
> +			  WDIOF_KEEPALIVEPING |
> +			  WDIOF_MAGICCLOSE,
> +};
> +
>  static const struct watchdog_ops mtk_wdt_ops = {
>  	.owner		= THIS_MODULE,
>  	.start		= mtk_wdt_start,
>  	.stop		= mtk_wdt_stop,
>  	.ping		= mtk_wdt_ping,
>  	.set_timeout	= mtk_wdt_set_timeout,
> +	.set_pretimeout	= mtk_wdt_set_pretimeout,
>  	.restart	= mtk_wdt_restart,
>  };
>  
> @@ -267,7 +305,7 @@ static int mtk_wdt_probe(struct platform_device *pdev)
>  	struct device *dev = &pdev->dev;
>  	struct mtk_wdt_dev *mtk_wdt;
>  	const struct mtk_wdt_data *wdt_data;
> -	int err;
> +	int err, irq;
>  
>  	mtk_wdt = devm_kzalloc(dev, sizeof(*mtk_wdt), GFP_KERNEL);
>  	if (!mtk_wdt)
> @@ -279,7 +317,22 @@ static int mtk_wdt_probe(struct platform_device *pdev)
>  	if (IS_ERR(mtk_wdt->wdt_base))
>  		return PTR_ERR(mtk_wdt->wdt_base);
>  
> -	mtk_wdt->wdt_dev.info = &mtk_wdt_info;
> +	irq = platform_get_irq(pdev, 0);
> +	if (irq > 0) {
> +		err = devm_request_irq(&pdev->dev, irq, mtk_wdt_isr, 0, "wdt_bark",
> +							&mtk_wdt->wdt_dev);
> +		if (err)
> +			return err;
> +
> +		mtk_wdt->wdt_dev.info = &mtk_wdt_pt_info;
> +		mtk_wdt->wdt_dev.pretimeout = 1;
> +	} else {
> +		if (irq == -EPROBE_DEFER)
> +			return -EPROBE_DEFER;
> +
> +		mtk_wdt->wdt_dev.info = &mtk_wdt_info;
> +	}
> +
>  	mtk_wdt->wdt_dev.ops = &mtk_wdt_ops;
>  	mtk_wdt->wdt_dev.timeout = WDT_MAX_TIMEOUT;
>  	mtk_wdt->wdt_dev.max_hw_heartbeat_ms = WDT_MAX_TIMEOUT * 1000;
> @@ -360,7 +413,6 @@ static struct platform_driver mtk_wdt_driver = {
>  };
>  
>  module_platform_driver(mtk_wdt_driver);
> -
>  module_param(timeout, uint, 0);
>  MODULE_PARM_DESC(timeout, "Watchdog heartbeat in seconds");
>  
>