linux-kernel - Re: [PATCH RFC 1/6] ARM: pxa: Convert Spitz OHCI to GPIO descriptors

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Date:   Sun, 1 Oct 2023 11:18:40 +0300
From:   Andy Shevchenko <andy@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Kent Gibson <warthog618@...il.com>,
        Duje Mihanović <duje.mihanovic@...le.hr>,
        Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Russell King <linux@...linux.org.uk>,
        Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH RFC 1/6] ARM: pxa: Convert Spitz OHCI to GPIO descriptors

On Wed, Sep 27, 2023 at 04:01:58PM +0200, Linus Walleij wrote:
> On Mon, Sep 25, 2023 at 9:30 AM Andy Shevchenko <andy@...nel.org> wrote:

...

> > > +     if (pxa_ohci->usb_host)
> > > +             gpiod_put(pxa_ohci->usb_host);
> >
> > Linus, Bart, do we have misdesigned _optinal() GPIO APIs?
> >
> > In GPIOLIB=n, the above requires that redundant check. Shouldn't we replace
> > gpiod_put() stub to be simply no-op?
> 
> You mean the WARN_ON(desc) in gpiod_put() in the static inline
> stub version?
> 
> I thought about it for a bit, drafted a patch removing them, and then
> realized the following:
> 
> If someone is making the gpiolib optional for a driver, i.e. neither
> DEPENDS ON GPIOLIB nor SELECT GPIOLIB, they are a quite
> narrow segment. I would say in 9 cases out of 10 or more this is
> just a driver that should depend on or select GPIOLIB.
> 
> I think such drivers should actually do the NULL checks and not be
> too convenient, the reason is readability: someone reading that
> driver will be thinking gpios are not optional if they can call
> gpiod_set_value(), gpiod_put() etc without any sign that the
> desc is optional.
> 
> If the driver uses [devm_]gpiod_get_optional() the library is not
> using the stubs and does the right thing, and it is clear that
> the GPIO is *runtime* optional.
> 
> But *compile time* optional, *combined* with runtime optional -
> I'm not so happy if we try to avoid warnings around that. I think
> it leads to confusing configs and code that looks like gpiolib is
> around despite it wasn't selected.
> 
> If the code isn't depending on or selecting GPIOLIB and still
> use _optional() calls, it better be ready to do some extra checks,
> because this is a weird combo, it can't be common.
> 
> Could be a documentation update making this clear though.
> 
> What do you other people think?

The problem here indeed if the code is not selecting or being dependent on
GPIOLIB and uses _optional() calls.

I agree that this is quite a niche that should be addressed on the driver side.

-- 
With Best Regards,
Andy Shevchenko