linux-kernel - Re: [PATCH 4/4] tty/serial: sh-sci: remove uneeded IS_ERR_OR

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Message-ID: <CAMuHMdXGn35bEsJKnUi5o3AytL4AJN2fBfoB79v5W-jOVFQx6g@mail.gmail.com>
Date:   Mon, 20 Mar 2017 10:56:14 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Richard Genoud <richard.genoud@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Janusz Uzycki <j.uzycki@...roma.com.pl>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH 4/4] tty/serial: sh-sci: remove uneeded IS_ERR_OR_NULL calls

Hi Linus,

On Thu, Mar 16, 2017 at 5:38 PM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
>> They actually all even do things like this in Kconfig:
>>
>> config SERIAL_ATMEL
>> (...)
>>         select SERIAL_MCTRL_GPIO if GPIOLIB
>>
>> What stops us from removing all the stubs in
>> drivers/tty/serial/serial_mctrl_gpio.h
>> and just make SERIAL_MCTRL_GPIO depends on GPIOLIB?
>
> Removing the stubs implies adding #ifdefs to the drivers that need
> to handle the !SERIAL_MCTRL_GPIO case.
>
> E.g. I don't want to break the sh-sci serial driver on SuperH platforms that
> (a) don't select GPIOLIB, and
> (b) don't use mtrl_gpio.

Alternatively, after commit 22c403676dbbb7c6 ("gpio: return NULL from
gpiod_get_optional when GPIOLIB is disabled") we might just drop the
dependency of SERIAL_MCTRL_GPIO on GPIOLIB? Then no special handling
is needed in drivers, as all GPIOs will just be considered not present.

Documentation/gpio/consumer.txt rightfully sates:
| Note that gpio_get*_optional() functions (and their managed variants), unlike
| the rest of gpiolib API, also return NULL when gpiolib support is disabled.
| This is helpful to driver authors, since they do not need to special case
| -ENOSYS return codes.  System integrators should however be careful to enable
| gpiolib on systems that need it.

drivers/tty/serial/serial_mctrl_gpio.o already compiles fine if
CONFIG_GPIOLIB=n, which reduces its size by ca. 25%.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds