linux-kernel - Re: [PATCH v4 12/15] pinctrl: Add AXP192 pin control driver

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Date:   Sat, 02 Jul 2022 20:22:58 +0100
From:   Aidan MacDonald <aidanmacdonald.0x0@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Sebastian Reichel <sre@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>, quic_gurus@...cinc.com,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        Michael Walle <michael@...le.cc>,
        Randy Dunlap <rdunlap@...radead.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v4 12/15] pinctrl: Add AXP192 pin control driver


Andy Shevchenko <andy.shevchenko@...il.com> writes:

> On Fri, Jul 1, 2022 at 5:36 PM Aidan MacDonald
> <aidanmacdonald.0x0@...il.com> wrote:
>> Andy Shevchenko <andy.shevchenko@...il.com> writes:
>> > On Wed, Jun 29, 2022 at 4:30 PM Aidan MacDonald
>> > <aidanmacdonald.0x0@...il.com> wrote:
>
> ...
>
>> >> +struct axp192_pctl_function {
>> >> +       const char              *name;
>> >> +       /* Mux value written to the control register to select the function (-1 if unsupported) */
>> >> +       const u8                *muxvals;
>> >> +       const char * const      *groups;
>> >> +       unsigned int            ngroups;
>> >> +};
>> >
>> > Can it be replaced by struct function_desc?
>> > https://elixir.bootlin.com/linux/latest/source/drivers/pinctrl/pinmux.h#L130
>>
>> That'd work, but using the generic infrastructure doesn't allow me to
>> simplify anything -- I can eliminate three trivial functions, but the
>> generic code is higher overhead (extra allocations, radix trees, ...)
>
> I really don't see how it gets into extra allocations. Either way you
> have a pointer to opaque data or in your current code it's called
> muxvals. Other fields seem 1:1 what is in struct function_desc. The
> code will be probably the same.
>
> I.o.w. I'm talking of eliminating data type, and not about simplifying
> the code by fully switching to generic infrastructure.

struct function_desc is hidden behind an #ifdef, so I can't use it
without enabling the generic pinmux helpers. It doesn't make a lot
of sense to enable them if they're not going to be used.

More generally, why would I use a type from an API I'm not using just
because it happens to look like a type I defined locally? That would
be misleading. Given that the code is the same either way, a local type
is preferable because it clearly communicates that I'm not using the
generic API, and guarantees that the type isn't referenced elsewhere.