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Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH V2] watchdog: mtk: support pre-timeout when the bark irq
 is available
To:     Wang Qing <wangqing@vivo.com>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        linux-watchdog@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org
References: <1618385339-3527-1-git-send-email-wangqing@vivo.com>
From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <427a4dc7-3528-83c6-b951-8ca0b2ca09a3@roeck-us.net>
Date:   Wed, 14 Apr 2021 04:23:36 -0700
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Precedence: bulk

On 4/14/21 12:28 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
> 
> Signed-off-by: Wang Qing <wangqing@vivo.com>
> ---
>  drivers/watchdog/mtk_wdt.c | 57 ++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 52 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/watchdog/mtk_wdt.c b/drivers/watchdog/mtk_wdt.c
> index 97ca993..b0ec933
> --- 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 +235,41 @@ 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);
> 


You said previously that the pretimeout would prevent the real timeout / reset
from happening, and the driver has no provision to set the real timeout.
That makes this a no-go.

>  	return 0;
>  }
>  
> +static int mtk_wdt_set_pretimeout(struct watchdog_device *wdd,
> +				   unsigned int timeout)
> +{
> +	wdd->pretimeout = timeout;
> +	return mtk_wdt_start(wdd);
> +}
> +
> +static irqreturn_t mtk_wdt_isr(int irq, void *arg)
> +{
> +	struct watchdog_device *wdd = arg;
> +if (IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_GOV))
> +	watchdog_notify_pretimeout(wdd);
> +else
> +	//panic by decault instead of WDT_SWRST;
> +	panic("MTk Watchdog bark!\n");
> +
The idea behind the pretimeout governor is that it can be disabled
by setting it to "none", and if pretimeout governors are disabled
it is supposed to be a no-op. The above bypasses this mechanism
and is not acceptable.

This suggests that the real timeout indeed doesn't happen when
WDT_MODE_IRQ_EN is set. Again, this is unacceptable.

On a side note, formatting is way off here.

Guenter

> +	return IRQ_HANDLED;
> +}
> +
>  static const struct watchdog_info mtk_wdt_info = {
>  	.identity	= DRV_NAME,
>  	.options	= WDIOF_SETTIMEOUT |
> @@ -253,12 +277,21 @@ 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 +300,7 @@ 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 +312,22 @@ 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 +408,6 @@ 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");
>  
>