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Sender: Guenter Roeck <groeck7@gmail.com>
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Date:   Mon, 24 Jan 2022 08:21:05 -0800
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To:     Alistair Francis <alistair@alistair23.me>,
        linux-arm-kernel@lists.infradead.org, shawnguo@kernel.org,
        linux-kernel@vger.kernel.org, s.hauer@pengutronix.de,
        linux-watchdog@vger.kernel.org, wim@linux-watchdog.org
Cc:     devicetree@vger.kernel.org, festevam@gmail.com, linux-imx@nxp.com,
        robh+dt@kernel.org, kernel@pengutronix.de
References: <20220124120027.106754-1-alistair@alistair23.me>
From:   Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH v2] watchdog: imx2_wdg: Alow ping on suspend
In-Reply-To: <20220124120027.106754-1-alistair@alistair23.me>
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On 1/24/22 04:00, Alistair Francis wrote:
> The i.MX watchdog cannot be disabled by softwrae once it has been

s/softwrae/software/

> enabled. This means that it can't be stopped before suspend.
> 
> For systems that enter low power mode this is fine, as the watchdog will
> be automatically stopped by hardwrae in low power mode. Not all i.MX

s/hardwrae/hardware/

> platforms support low power mode in the mainline kernel. For example the
> i.MX7D does not enter low power mode and so will be rebooted 2 minutes
> after entering freeze or mem sleep states.

I don't think "mem" adds any value here. Just make it sleep states.

> 
> This patch introduces a device tree property "fsl,ping-during-suspend"
> that can be used to enable ping on suspend support for these systems.
> 
> Signed-off-by: Alistair Francis <alistair@alistair23.me>
> ---

Change log goes here.

>   drivers/watchdog/imx2_wdt.c | 27 ++++++++++++++++++++-------
>   1 file changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
> index 51bfb796898b..d0c5d47ddede 100644
> --- a/drivers/watchdog/imx2_wdt.c
> +++ b/drivers/watchdog/imx2_wdt.c
> @@ -66,6 +66,7 @@ struct imx2_wdt_device {
>   	struct watchdog_device wdog;   
>   	bool ext_reset;
>   	bool clk_is_on;

I don't see the purpose of this variable. Unless I am missing something is is set
but never used.

> +	bool no_ping;
>   };
>   
>   static bool nowayout = WATCHDOG_NOWAYOUT;
> @@ -312,12 +313,18 @@ static int __init imx2_wdt_probe(struct platform_device *pdev)
>   
>   	wdev->ext_reset = of_property_read_bool(dev->of_node,
>   						"fsl,ext-reset-output");
> +	/*
> +	 * The i.MX7D doesn't support low power mode, so we need to ping the watchdog
> +	 * during suspend.
> +	 */
> +	wdev->no_ping = !of_device_is_compatible(dev->of_node, "fsl,imx7d-wdt");

This is ok as long as there is only a single chip requiring this change.
If there are more, the 'data' field in struct of_device_id should be used
instead.

>   	platform_set_drvdata(pdev, wdog);
>   	watchdog_set_drvdata(wdog, wdev);
>   	watchdog_set_nowayout(wdog, nowayout);
>   	watchdog_set_restart_priority(wdog, 128);
>   	watchdog_init_timeout(wdog, timeout, dev);
> -	watchdog_stop_ping_on_suspend(wdog);
> +	if (wdev->no_ping)
> +		watchdog_stop_ping_on_suspend(wdog);
>   
>   	if (imx2_wdt_is_running(wdev)) {
>   		imx2_wdt_set_timeout(wdog, wdog->timeout);
> @@ -366,9 +373,11 @@ static int __maybe_unused imx2_wdt_suspend(struct device *dev)
>   		imx2_wdt_ping(wdog);
>   	}
>   
> -	clk_disable_unprepare(wdev->clk);
> +	if (wdev->no_ping) {
> +		clk_disable_unprepare(wdev->clk);
>   
> -	wdev->clk_is_on = false;
> +		wdev->clk_is_on = false;
> +	}
>   
>   	return 0;
>   }
> @@ -380,11 +389,14 @@ static int __maybe_unused imx2_wdt_resume(struct device *dev)
>   	struct imx2_wdt_device *wdev = watchdog_get_drvdata(wdog);
>   	int ret;
>   
> -	ret = clk_prepare_enable(wdev->clk);
> -	if (ret)
> -		return ret;
> +	if (wdev->no_ping) {
> +		ret = clk_prepare_enable(wdev->clk);
>   
> -	wdev->clk_is_on = true;
> +		if (ret)
> +			return ret;
> +
> +		wdev->clk_is_on = true;
> +	}
>   
>   	if (watchdog_active(wdog) && !imx2_wdt_is_running(wdev)) {
>   		/*
> @@ -407,6 +419,7 @@ static SIMPLE_DEV_PM_OPS(imx2_wdt_pm_ops, imx2_wdt_suspend,
>   
>   static const struct of_device_id imx2_wdt_dt_ids[] = {
>   	{ .compatible = "fsl,imx21-wdt", },
> +	{ .compatible = "fsl,imx7d-wdt", },
>   	{ /* sentinel */ }
>   };
>   MODULE_DEVICE_TABLE(of, imx2_wdt_dt_ids);