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Date:   Mon, 5 Sep 2022 15:07:48 -0700
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To:     Andy Shevchenko <andy.shevchenko@gmail.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>
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From:   Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH v1 04/11] usb: phy: tegra: switch to using
 devm_gpiod_get()
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On 9/5/22 12:55, Andy Shevchenko wrote:
> On Mon, Sep 5, 2022 at 10:51 PM Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
>> On Mon, Sep 05, 2022 at 10:41:40PM +0300, Andy Shevchenko wrote:
>>> On Mon, Sep 5, 2022 at 10:40 PM Dmitry Torokhov
>>> <dmitry.torokhov@gmail.com> wrote:
>>>> On Mon, Sep 05, 2022 at 01:59:44PM +0300, Andy Shevchenko wrote:
>>>>> On Mon, Sep 5, 2022 at 9:32 AM Dmitry Torokhov
>>>>> <dmitry.torokhov@gmail.com> wrote:
> 
> ...
> 
>>>>>> -               gpiod = devm_gpiod_get_from_of_node(&pdev->dev, np,
>>>>>> -                                                   "nvidia,phy-reset-gpio",
>>>>>> -                                                   0, GPIOD_OUT_HIGH,
>>>>>> -                                                   "ulpi_phy_reset_b");
>>>>>> +               gpiod = devm_gpiod_get(&pdev->dev, "nvidia,phy-reset",
>>>>>> +                                      GPIOD_OUT_HIGH);
>>>>>>                  err = PTR_ERR_OR_ZERO(gpiod);
>>>>>
>>>>> What does _OR_ZERO mean now?
>>>>
>>>> This converts a pointer to an error code if a pointer represents
>>>> ERR_PTR() encoded error, or 0 to indicate success.
>>>
>>> Yes, I know that. My point is, how is it useful now (or even before)?
>>> I mean that devm_gpio_get() never returns NULL, right?
>>
>> What does returning NULL have to do with anything.
> 
> It has to do with a dead code. If defm_gpiod_get() does not return
> NULL, then why do we even bother to check?
> 

PTR_ERR_OR_ZERO() converts into an error code (if the pointer is an
ERR_PTR) or 0 if it is a real pointer. Its purpose is not to convert
NULL into 0, its purpose is to convert a pointer either into an error
code or 0. That is what is done here, and it is done all over the place
in the kernel. I don't see your problem with it. Care to explain ?

>> It converts a pointer
>> to a "classic" return code, with negative errors and 0 on success.
>>
>> It allows to not use multiple IS_ERR/PTR_ERR in the code (I'd need 1
>> IS_ERR and 2 PTR_ERR, one in dev_err() and another to return).
> 
> I don't see how this is relevant.
> 

You lost me. Really, please explain your problem with PTR_ERR_OR_ZERO().

Thanks,
Guenter