linux-kernel - Re: [PATCH 1/2] tty: serial: samsung

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Date:   Tue, 25 Feb 2020 22:22:11 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Donghoon Yu <hoony.yu@...sung.com>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Shinbeom Choi <sbeom.choi@...sung.com>,
        Hyunki Koo <kkoos00@...er.com>, Kukjin Kim <kgene@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>,
        HYUN-KI KOO <hyunki00.koo@...sung.com>
Subject: Re: [PATCH 1/2] tty: serial: samsung_tty: build it for any platform

Hi Greg,

On Tue, Feb 25, 2020 at 9:41 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Tue, Feb 25, 2020 at 09:52:38AM +0100, Geert Uytterhoeven wrote:
> > On Thu, Feb 20, 2020 at 1:13 PM Bartlomiej Zolnierkiewicz
> > <b.zolnierkie@...sung.com> wrote:
> > > On 2/20/20 11:26 AM, Greg Kroah-Hartman wrote:
> > > > There is no need to tie this driver to only a specific SoC, or compile
> > > > test, so remove that dependancy from the Kconfig rules.
> > >
> > > samsung_tty driver is hardware specific driver so why should we
> > > build it for any platform?
>
> Why not?

Because this driver won't bind to a device anyway, when the kernel is
configured without Samsung SoC support.  It will just bloat the kernel,
and asking this question is a silly waste of time for anyone building a
(non-generic) kernel for a non-Samsung SoC.

> Seriously, this "only this one specific SoC is allowed to build this
> driver" is crazy.  It prevents anyone from building a generic kernel
> with drivers as a module which are loaded as needed.

A generic kernel will include Samsung SoC support, hence PLAT_SAMSUNG
or ARCH_EXYNOS will be enabled.

> That needs to be fixed, and removing this unneeded dependancy on this
> driver allows it to be build for any system and then only loaded when
> needed.

It can only be loaded on a Samsung system, which requires PLAT_SAMSUNG
or ARCH_EXYNOS anyway.
It's not like a Samsung serial device can be plugged into your PC's PCI
bus or so, it only exists on Samsung SoCs.

> > > This change seems to defeat the whole purpose behind COMPILE_TEST
> > > config option (which allows us to build hardware-specific drivers
> > > without needlessly presenting the user with tons of non-relevant
> > > config options).
> > >
> > > Please explain this change some more, are you planing to remove
> > > COMPILE_TEST config option?
>
> I want to get rid of this:

IMHO we need _more_ of these dependencies, to avoid all these silly questions
when they don't make sense.

> > > > -     depends on PLAT_SAMSUNG || ARCH_EXYNOS || COMPILE_TEST
>
> We should not need PLAT_SAMSUNG or ARCH_EXYNOS at all, we should be able
> to build an arm64 kernel for all platforms.

An arm64 kernel for all platforms will have ARCH_EXYNOS enabled.

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