linux-kernel - Re: [PATCH v2] watchdog: qcom_wdt: set WDOG_HW

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Date:   Fri, 30 Oct 2020 10:51:24 +0530
From:   kathirav@...eaurora.org
To:     Robert Marko <robert.marko@...tura.hr>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org,
        wim@...ux-watchdog.org, linux@...ck-us.net,
        linux-arm-msm@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Luka Perkov <luka.perkov@...tura.hr>" <kathirav@...eaurora.org>
Subject: Re: [PATCH v2] watchdog: qcom_wdt: set WDOG_HW_RUNNING bit when
 appropriate

On 2020-10-28 17:16, Robert Marko wrote:
> If the watchdog hardware is enabled/running during boot, e.g.
> due to a boot loader configuring it, we must tell the
> watchdog framework about this fact so that it can ping the
> watchdog until userspace opens the device and takes over
> control.
> 
> Do so using the WDOG_HW_RUNNING flag that exists for exactly
> that use-case.
> 
> Given the watchdog driver core doesn't know what timeout was
> originally set by whoever started the watchdog (boot loader),
> we make sure to update the timeout in the hardware according
> to what the watchdog core thinks it is.
> 
> Signed-off-by: Robert Marko <robert.marko@...tura.hr>
> Cc: Luka Perkov <luka.perkov@...tura.hr>
> ---
> Changes in v2:
> * Correct authorship
> 
>  drivers/watchdog/qcom-wdt.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> index ab7465d186fd..28c93a918e38 100644
> --- a/drivers/watchdog/qcom-wdt.c
> +++ b/drivers/watchdog/qcom-wdt.c
> @@ -152,6 +152,13 @@ static int qcom_wdt_restart(struct
> watchdog_device *wdd, unsigned long action,
>  	return 0;
>  }
> 
> +static int qcom_wdt_is_running(struct watchdog_device *wdd)
> +{
> +	struct qcom_wdt *wdt = to_qcom_wdt(wdd);
> +
> +	return (readl(wdt_addr(wdt, WDT_EN)) & 1);

QCOM_WDT_ENABLE macro can be used instead of 1?

> +}
> +
>  static const struct watchdog_ops qcom_wdt_ops = {
>  	.start		= qcom_wdt_start,
>  	.stop		= qcom_wdt_stop,
> @@ -294,6 +301,21 @@ static int qcom_wdt_probe(struct platform_device 
> *pdev)
>  	wdt->wdd.timeout = min(wdt->wdd.max_timeout, 30U);
>  	watchdog_init_timeout(&wdt->wdd, 0, dev);
> 
> +	if (qcom_wdt_is_running(&wdt->wdd)) {
> +		/*
> +		 * Make sure to apply timeout from watchdog core, taking
> +		 * the prescaler of this driver here into account (the
> +		 * boot loader might be using a different prescaler).
> +		 *
> +		 * To avoid spurious resets because of different scaling,
> +		 * we first disable the watchdog, set the new prescaler
> +		 * and timeout, and then re-enable the watchdog.
> +		 */
> +		qcom_wdt_stop(&wdt->wdd);

qcom_wdt_start disables the WDT, configure the timeout values and 
enables it. Do we still need to call qcom_wdt_stop?

> +		qcom_wdt_start(&wdt->wdd);
> +		set_bit(WDOG_HW_RUNNING, &wdt->wdd.status);
> +	}
> +
>  	ret = devm_watchdog_register_device(dev, &wdt->wdd);
>  	if (ret)
>  		return ret;