linux-kernel - Re: [PATCH v1 04/11] usb: phy: tegra: switch to using devm_gpiod

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Message-ID: <4a0d089d-6ac6-b92e-6ac7-3d3de0144b4b@roeck-us.net>
Date:   Mon, 5 Sep 2022 15:07:48 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Matti Vaittinen <mazziesaccount@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Felipe Balbi <balbi@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Marc Zyngier <maz@...nel.org>,
        Richard Weinberger <richard@....at>,
        David Airlie <airlied@...ux.ie>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Rob Herring <robh@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Pali Rohár <pali@...nel.org>,
        LINUXWATCHDOG <linux-watchdog@...r.kernel.org>,
        USB <linux-usb@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        "open list:MEMORY TECHNOLOGY..." <linux-mtd@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v1 04/11] usb: phy: tegra: switch to using
 devm_gpiod_get()

On 9/5/22 12:55, Andy Shevchenko wrote:
> On Mon, Sep 5, 2022 at 10:51 PM Dmitry Torokhov
> <dmitry.torokhov@...il.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@...il.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@...il.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