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

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Message-ID: <27d4ec69-1744-4421-0d34-924d14b3c1e6@samsung.com>
Date:   Wed, 26 Feb 2020 11:11:11 +0100
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     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


On 2/25/20 10:22 PM, Geert Uytterhoeven wrote:
> 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.

+1 on all comments from Geert

IMHO this change should be reverted (it doesn't fix anything and
only makes kernel configuration harder).

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics