linux-kernel - Re: [PATCH 2/2] watchdog: rti_wdt: Drop RPM watchdog when unused

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Date:   Fri, 10 Nov 2023 07:05:18 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Vignesh Raghavendra <vigneshr@...com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>
Cc:     Tero Kristo <t-kristo@...nel.org>, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        afd@...com, n-francis@...com
Subject: Re: [PATCH 2/2] watchdog: rti_wdt: Drop RPM watchdog when unused

On 11/10/23 02:07, Vignesh Raghavendra wrote:
> Do a RPM put if watchdog is not already started during probe and re
> enable it in watchdog start.
> 
> On K3 SoCs, watchdogs and their corresponding CPUs are under same PD, so
> if the reference count of unused watchdogs aren't dropped, it will lead
> to CPU hotplug failures as Device Management firmware won't allow to
> turn off the PD due to dangling reference count.
> 
> Fixes: 2d63908bdbfb ("watchdog: Add K3 RTI watchdog support")
> Signed-off-by: Vignesh Raghavendra <vigneshr@...com>
> ---
>   drivers/watchdog/rti_wdt.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> index 163bdeb6929a..87f2c333a41d 100644
> --- a/drivers/watchdog/rti_wdt.c
> +++ b/drivers/watchdog/rti_wdt.c
> @@ -78,6 +78,9 @@ static int rti_wdt_start(struct watchdog_device *wdd)
>   	u32 timer_margin;
>   	struct rti_wdt_device *wdt = watchdog_get_drvdata(wdd);
>   
> +	if (pm_runtime_suspended(wdd->parent))
> +		pm_runtime_get_sync(wdd->parent);
> +
>   	/* set timeout period */
>   	timer_margin = (u64)wdd->timeout * wdt->freq;
>   	timer_margin >>= WDT_PRELOAD_SHIFT;
> @@ -337,6 +340,9 @@ static int rti_wdt_probe(struct platform_device *pdev)
>   	if (last_ping)
>   		watchdog_set_last_hw_keepalive(wdd, last_ping);
>   
> +	if (!watchdog_hw_running(wdd))
> +		pm_runtime_put_sync(&pdev->dev);
> +

You will have to explain why this is needed here, but not as error handling,
and why it is added in this patch after the changes in patch 1 of the series
which essentially declared that no error cleanup would be needed under
any circumstances.

Guenter

>   	return 0;
>   }
>   
> @@ -345,6 +351,9 @@ static void rti_wdt_remove(struct platform_device *pdev)
>   	struct rti_wdt_device *wdt = platform_get_drvdata(pdev);
>   
>   	watchdog_unregister_device(&wdt->wdd);
> +
> +	if (!pm_runtime_suspended(&pdev->dev))
> +		pm_runtime_put_sync(&pdev->dev);
>   }
>   
>   static const struct of_device_id rti_wdt_of_match[] = {