linux-kernel - Re: [PATCH 1/2] watchdog: rti_wdt: Use managed APIs to handle runtime PM

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Message-ID: <40590367-0a38-4c4c-a608-1174a5ecd5ae@roeck-us.net>
Date:   Fri, 10 Nov 2023 07:03:25 -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 1/2] watchdog: rti_wdt: Use managed APIs to handle runtime
 PM

On 11/10/23 02:07, Vignesh Raghavendra wrote:
> Switch to devm_pm_runtime_enable() to simplify error handling in driver
> probe.
> 

This also replaces the call to pm_runtime_resume_and_get() without explanation.
Worse, the next patch conditionally re-introduces pm_runtime_put_sync()
on the probe function.

> Signed-off-by: Vignesh Raghavendra <vigneshr@...com>
> ---
>   drivers/watchdog/rti_wdt.c | 30 ++++++++----------------------
>   1 file changed, 8 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> index 8e1be7ba0103..163bdeb6929a 100644
> --- a/drivers/watchdog/rti_wdt.c
> +++ b/drivers/watchdog/rti_wdt.c
> @@ -236,12 +236,8 @@ static int rti_wdt_probe(struct platform_device *pdev)
>   	if (wdt->freq < 32768)
>   		wdt->freq = wdt->freq * 9 / 10;
>   
> -	pm_runtime_enable(dev);
> -	ret = pm_runtime_resume_and_get(dev);
> -	if (ret < 0) {
> -		pm_runtime_disable(&pdev->dev);
> -		return dev_err_probe(dev, ret, "runtime pm failed\n");
> -	}
> +	devm_pm_runtime_enable(dev);

devm_pm_runtime_enable() returns an error code. I don't think ignoring it
is a good idea.

> +	pm_runtime_get_noresume(dev);

Is this functionally identical to pm_runtime_resume_and_get() ?
That would require further explanation. Why is it not necessary
to resume here ?

Also, doesn't the next patch fix or at least modify this ?

>   
>   	platform_set_drvdata(pdev, wdt);
>   
> @@ -260,7 +256,7 @@ static int rti_wdt_probe(struct platform_device *pdev)
>   	wdt->base = devm_platform_ioremap_resource(pdev, 0);
>   	if (IS_ERR(wdt->base)) {
>   		ret = PTR_ERR(wdt->base);
> -		goto err_iomap;
> +		return ret;
>   	}
>   
>   	if (readl(wdt->base + RTIDWDCTRL) == WDENABLE_KEY) {
> @@ -286,7 +282,7 @@ static int rti_wdt_probe(struct platform_device *pdev)
>   		ret = rti_wdt_setup_hw_hb(wdd, wsize);
>   		if (ret) {
>   			dev_err(dev, "bad window size.\n");
> -			goto err_iomap;
> +			return ret;
>   		}
>   
>   		last_ping = heartbeat_ms - time_left_ms;
> @@ -301,7 +297,7 @@ static int rti_wdt_probe(struct platform_device *pdev)
>   		ret = of_address_to_resource(node, 0, &res);
>   		if (ret) {
>   			dev_err(dev, "No memory address assigned to the region.\n");
> -			goto err_iomap;
> +			return ret;
>   		}
>   
>   		/*
> @@ -312,15 +308,13 @@ static int rti_wdt_probe(struct platform_device *pdev)
>   		reserved_mem_size = resource_size(&res);
>   		if (reserved_mem_size < RESERVED_MEM_MIN_SIZE) {
>   			dev_err(dev, "The size of reserved memory is too small.\n");
> -			ret = -EINVAL;
> -			goto err_iomap;
> +			return -EINVAL;
>   		}
>   
>   		vaddr = memremap(paddr, reserved_mem_size, MEMREMAP_WB);
>   		if (!vaddr) {
>   			dev_err(dev, "Failed to map memory-region.\n");
> -			ret = -ENOMEM;
> -			goto err_iomap;
> +			return -ENOMEM;
>   		}
>   
>   		if (vaddr[0] == PON_REASON_SOF_NUM &&
> @@ -337,19 +331,13 @@ static int rti_wdt_probe(struct platform_device *pdev)
>   	ret = watchdog_register_device(wdd);
>   	if (ret) {
>   		dev_err(dev, "cannot register watchdog device\n");
> -		goto err_iomap;
> +		return ret;
>   	}
>   
>   	if (last_ping)
>   		watchdog_set_last_hw_keepalive(wdd, last_ping);
>   
>   	return 0;
> -
> -err_iomap:
> -	pm_runtime_put_sync(&pdev->dev);
> -	pm_runtime_disable(&pdev->dev);
> -
> -	return ret;
>   }
>   
>   static void rti_wdt_remove(struct platform_device *pdev)
> @@ -357,8 +345,6 @@ static void rti_wdt_remove(struct platform_device *pdev)
>   	struct rti_wdt_device *wdt = platform_get_drvdata(pdev);
>   
>   	watchdog_unregister_device(&wdt->wdd);
> -	pm_runtime_put(&pdev->dev);
> -	pm_runtime_disable(&pdev->dev);
>   }
>   
>   static const struct of_device_id rti_wdt_of_match[] = {