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

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Date:   Tue, 6 Sep 2022 15:27:31 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        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>,
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        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>,
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        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 Mon, Sep 05, 2022 at 03:07:48PM -0700, Guenter Roeck wrote:
> 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(&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().

I don't know what I was thinking about... You, guys, are right, sorry for
my noise.

-- 
With Best Regards,
Andy Shevchenko