linux-kernel - Re: [PATCH v2 13/14] usb: host: ehci-st: simplify optional reset handling

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Date:   Wed, 15 Mar 2017 10:35:01 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Philipp Zabel <p.zabel@...gutronix.de>
cc:     linux-usb@...r.kernel.org,
        Patrice Chotard <patrice.chotard@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 13/14] usb: host: ehci-st: simplify optional reset
 handling

On Wed, 15 Mar 2017, Philipp Zabel wrote:

> As of commit bb475230b8e5 ("reset: make optional functions really
> optional"), the reset framework API calls use NULL pointers to describe
> optional, non-present reset controls.

What does it use to describe genuine errors?

> This allows to return errors from devm_reset_control_get_optional_shared
> unconditionally.
> 
> Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
> ---
>  drivers/usb/host/ehci-st.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/usb/host/ehci-st.c b/drivers/usb/host/ehci-st.c
> index be4a2788fc582..12e803d2c98df 100644
> --- a/drivers/usb/host/ehci-st.c
> +++ b/drivers/usb/host/ehci-st.c
> @@ -210,18 +210,14 @@ static int st_ehci_platform_probe(struct platform_device *dev)
>  		devm_reset_control_get_optional_shared(&dev->dev, "power");
>  	if (IS_ERR(priv->pwr)) {
>  		err = PTR_ERR(priv->pwr);
> -		if (err == -EPROBE_DEFER)
> -			goto err_put_clks;
> -		priv->pwr = NULL;
> +		goto err_put_clks;
>  	}
>  
>  	priv->rst =
>  		devm_reset_control_get_optional_shared(&dev->dev, "softreset");
>  	if (IS_ERR(priv->rst)) {
>  		err = PTR_ERR(priv->rst);
> -		if (err == -EPROBE_DEFER)
> -			goto err_put_clks;
> -		priv->rst = NULL;
> +		goto err_put_clks;
>  	}
>  
>  	if (pdata->power_on) {

These changes do not agree with the patch description.  If any sort of 
error besides EPROBE_DEFER occurs then:

	the old code sets priv->pwr or priv->rst to NULL and continues;

	the new code returns with an error.

The only way the patch could be equivalent to the existing code would
be if devm_reset_control_get_optional_shared() returns no errors other
than EPROBE_DEFER.  But the patch description doesn't say this.

Alan Stern