linux-kernel - Re: [PATCH v5 2/2] pinctrl: Add driver for Sunplus SP7021

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Date:   Thu, 13 Jan 2022 20:04:28 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Wells Lu 呂芳騰 <wells.lu@...plus.com>
Cc:     Wells Lu <wellslutw@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        "dvorkin@...bo.com" <dvorkin@...bo.com>
Subject: Re: [PATCH v5 2/2] pinctrl: Add driver for Sunplus SP7021

On Thu, Jan 13, 2022 at 7:04 PM Wells Lu 呂芳騰 <wells.lu@...plus.com> wrote:

...

> > > > > +       bool "Sunplus SP7021 PinMux and GPIO driver"
> > > >
> > > > Why bool and not tristate?
> > >
> > > Pinctrl driver is selected by many drivers in SP7021 platform.
> > > We never build it as a module, but build-in to kernel.
> > > So we use "bool".
> > >
> > > Should we set it to tristate?
> >
> > You still haven't answered "why", so I can't tell you.
>
> I am puzzled because I think I have answered "why".

Nope. :-)

> Because Pinctrl driver is necessary for all SP7021-based platforms.

"Why?" Why is it necessary (to be built-in)?

...

> > > > > +       struct device_node *np = of_node_get(pdev->dev.of_node);
> > > >
> > > > What's the role of of_node_get()?
> > >
> > > I'll remove the unused codes.
> > > I think it was used to check if OF node exists.
> >
> > And if it doesn't, what is the difference?
> >
> > You are the author of this code, please be prepared to explain every line in it.
>
> From kernel-doc comment, of_node_get() increments refcount of a node.
> I think as a platform driver, we don't need to check if the node exists or not.
> If not exist, platform driver will not be probed.

Right!

...

> > > > Why is this in the header?
> > >
> > > Do you mean I need to move this "struct sppctl_gpio_chip { ... }"
> > > declaration to c file because it is only used by the c file?
> >
> > Yes.
>
> But "struct sppctl_gpio_chip" is not only used in c file, but also used in the
> same header file just beneath it. Refer to code below:

Thanks for the snippet. It actually shows the opposite. No, below is
the user of the _pointer_ to the struct of that type. You may easily
use the "opaque pointer" approach. I.o.w. my comment stays.

> struct sppctl_gpio_chip {
>         :
>         :
> };
>
> struct sppctl_pdata {
>         :
>         :
>         struct sppctl_gpio_chip *spp_gchip;
>         :
>         :
> };

-- 
With Best Regards,
Andy Shevchenko