Re: [PATCH 5/9] gpio: mxc: use devres-managed PM runtime and dev_err_probe

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] gpio: mxc: PM usage counter underflow due to devm_pm_runtime_get_noresume and manual put
- [High] gpio: mxc: ignored devm_pm_runtime_enable and get_noresume returns
--

commit e443f1e5bd54a410ade428061ede6f400132fc30
Author: Peng Fan <peng.fan@nxp.com>

gpio: mxc: use devres-managed PM runtime and dev_err_probe

This patch switches the driver to use devres-managed PM runtime functions
and replaces goto error paths with direct returns using dev_err_probe().

> diff --git a/drivers/gpio/gpio-mxc.c b/drivers/gpio/gpio-mxc.c
> index 3c395c82d7d46..73e19d2bf2351 100644
> --- a/drivers/gpio/gpio-mxc.c
> +++ b/drivers/gpio/gpio-mxc.c
> @@ -474,9 +474,9 @@ static int mxc_gpio_probe(struct platform_device *pdev)
>  	if (of_device_is_compatible(np, "fsl,imx8qm-gpio"))
>  		port->is_imx8qm = true;
>  
> -	pm_runtime_get_noresume(&pdev->dev);
> +	devm_pm_runtime_get_noresume(&pdev->dev);
>  	pm_runtime_set_active(&pdev->dev);
> -	pm_runtime_enable(&pdev->dev);
> +	devm_pm_runtime_enable(&pdev->dev);

[Severity: High]
Should the return values of devm_pm_runtime_get_noresume() and
devm_pm_runtime_enable() be checked?

Both functions allocate memory for devres actions and can return error codes
like -ENOMEM. If devm_pm_runtime_get_noresume() fails, it drops its reference
internally by calling pm_runtime_put_noidle(). 

If we ignore this failure and continue, the probe proceeds under the false
assumption that it holds a PM reference. The manual call to
pm_runtime_put_autosuspend() at the end of mxc_gpio_probe() would then
immediately underflow the PM usage counter.

[ ... ]

> @@ -552,12 +548,6 @@ static int mxc_gpio_probe(struct platform_device *pdev)
>  	pm_runtime_put_autosuspend(&pdev->dev);

[Severity: High]
Will this result in a PM usage counter underflow when the device is unbound?

Because devm_pm_runtime_get_noresume() registers a devres action to call
pm_runtime_put_noidle() on device unbind, the initial reference is already
managed. By manually calling pm_runtime_put_autosuspend() here at the end
of probe to enter autosuspend, the usage counter is decremented early. 

When the device is subsequently unregistered or unbound, the devres cleanup
will execute and drop the already zeroed usage counter, causing a kernel
warning.

>  
>  	return 0;
> -
> -out_bgio:
> -	pm_runtime_disable(&pdev->dev);
> -	pm_runtime_put_noidle(&pdev->dev);
> -	dev_info(&pdev->dev, "%s failed with errno %d\n", __func__, err);
> -	return err;
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261003-gpio-mxc-cleanup-v1-0-dad728ce27f2@nxp.com?part=5