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

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Sep 25, 2023 at 9:30 AM Andy Shevchenko <andy@xxxxxxxxxx> 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?

Yours,
Linus Walleij