From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Cc: Saravana Kannan <saravanak@google.com>,
Lee Jones <lee.jones@linaro.org>,
Will McVicker <willmcvicker@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Sylwester Nawrocki <s.nawrocki@samsung.com>,
Tomasz Figa <tomasz.figa@gmail.com>,
Chanwoo Choi <cw00.choi@samsung.com>,
Michael Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@kernel.org>,
Linus Walleij <linus.walleij@linaro.org>,
Alessandro Zummo <a.zummo@towertech.it>,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
Android Kernel Team <kernel-team@android.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
linux-clk <linux-clk@vger.kernel.org>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
linux-rtc@vger.kernel.org, Kevin Hilman <khilman@baylibre.com>
Subject: Re: [PATCH v1 0/4] arm64: Kconfig: Update ARCH_EXYNOS select configs
Date: Mon, 27 Sep 2021 10:16:12 +0200 [thread overview]
Message-ID: <CAMuHMdXU=BKJugMXggyZYBUd+fB7CSd8F5iCWqcBw894OZCZHQ@mail.gmail.com> (raw)
In-Reply-To: <5ec72235-add4-d6dd-f89f-ca3941c9878e@canonical.com>
Hi Krzysztof,
On Mon, Sep 27, 2021 at 10:08 AM Krzysztof Kozlowski
<krzysztof.kozlowski@canonical.com> wrote:
> On 25/09/2021 04:17, Saravana Kannan wrote:
> > On Tue, Sep 21, 2021 at 1:25 AM Krzysztof Kozlowski
> > <krzysztof.kozlowski@canonical.com> wrote:
> >> On 21/09/2021 10:11, Lee Jones wrote:
> >>> On Tue, 21 Sep 2021, Krzysztof Kozlowski wrote:
> >>>> On 20/09/2021 21:03, Will McVicker wrote:
> >>>>> This patch series tries to address the issue of ARCH_EXYNOS force selecting
> >>>>> a handful of drivers without allowing the vendor to override any of the
> >>>>> default configs. This takes away from the flexibilty of compiling a generic
> >>>>> kernel with exynos kernel modules. For example, it doesn't allow vendors to
> >>>>> modularize these drivers out of the core kernel in order to share a generic
> >>>>> kernel image across multiple devices that require device-specific kernel
> >>>>> modules.
> >>>>
> >>>> You do not address the issue in these patches. The problem you describe
> >>>> is that drivers are not modules and you are not changing them into modules.
> >>>
> >>> The wording is unfortunate. The reason for this change doesn't have
> >>> much to do with kernel modules.
> >>>
> >>> Let's go back in time 18 months or so when Greg KH submitted this [0]
> >>> patch, which you Acked. Greg was trying to solve the problem of not
> >>> having to enable ARCH_EXYNOS on kernels which are designed to be
> >>> platform agnostic (sometimes called Generic Kernels). For some reason
> >>> SERIAL_SAMSUNG is the only symbol with these dependencies, so the
> >>> solution seemed simple and straight forward at the time.
> >>>
> >>> However, For sound reasons Geert NACKed the patch.
> >>>
> >>> Quoting from [1] he says:
> >>>
> >>> "A generic kernel will include Samsung SoC support, hence
> >>> PLAT_SAMSUNG or ARCH_EXYNOS will be enabled."
> >>
> >> Yes, it's correct reasoning. There is also one more use-case -
> >> non-upstreamed (out of tree) platform which wants to use Exynos-specific
> >> drivers. Something like was happening with Apple M1 except that it got
> >> upstreamed and we do not care much about out-of-tree.
> >>
> >>> However, since the entry for ARCH_EXYNOS *insists* on building-in a
> >>> bunch of other symbols (via 'select') which will be unused in most
> >>> cases, this is not a currently acceptable approach for many Generic
> >>> Kernels due to size constraints.
> >>
> >> In the mainline kernel there is no such use case. If you want to have
> >> Exynos-whatever-driver (e.g. SERIAL_SAMSUNG or S3C RTC), you should
> >> select ARCH_EXYNOS because otherwise it does not make any sense. Zero
> >> sense. Such kernel won't work.
> >>
> >> It makes sense only if there is some other work, hidden here, where
> >> someone might want to have SERIAL_SAMSUNG or S3C RTC without
> >> ARCH_EXYNOS. Although GKI is not that work because GKI kernel will
> >> select ARCH_EXYNOS. It must select ARCH_EXYNOS if it wants to support
> >> Exynos platforms.
> >>
> >> Therefore I expect first to bring this "some other work, hidden here" to
> >> broader audience, so we can review its use case.
> >>
> >>> What this patch does is migrates those symbols from being 'select'ed
> >>> (always built-in with no recourse) to 'default y'. Where the former
> >>> cannot be over-ridden, but the latter can be via a vendor's
> >>> defconfig/fragment.
> >>
> >> It cannot be overridden by vendor fragment because options are not
> >> visible. You cannot change them.
> >>
> >> The patch does nothing in this regard (making them selectable/possible
> >> to disable), which is why I complained.
> >>
> >>> I doubt many (any?) of these symbols can be converted to kernel
> >>> modules anyway, as they are required very early on in the boot
> >>> sequence.
> >>
> >> True, some could, some not. Also some platforms are set up via
> >> bootloader, so actually could "survive" till module is loaded from some
> >> initrd.
> >
> > I was trying to chime in, but the discussion got spread out across all
> > the patches. Since the cover letter seems to have everyone, I thought
> > I'd reply here. Hope you don't mind. I'll try to respond/chime in on
> > the various topics that were raised across the patches.
> >
> > Yes, the next patch series would To/Cc folks correctly. William simply
> > forgot to use the --to-cover and --cc-cover options when using git
> > send-email.
> >
> > I agree with you that it doesn't make sense to have ARCH_EXYNOS
> > enabled but to have all the clock drivers exynos compiled out. Then
> > one obviously can't boot an exynos platform using that kernel.
>
> If downstream kernel does not use any upstream platforms (e.g.
> Exynos5433 or Exynos7) and has its own drivers for everything, then
> downstream does not even need ARCH_EXYNOS. Just disable it.
I guess that's how they got to "[PATCH 1/2] tty: serial: samsung_tty:
build it for any platform"...
https://lore.kernel.org/lkml/20200220102628.3371996-1-gregkh@linuxfoundation.org/
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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
next prev parent reply other threads:[~2021-09-27 8:16 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-20 19:03 [PATCH v1 0/4] arm64: Kconfig: Update ARCH_EXYNOS select configs Will McVicker
2021-09-20 19:03 ` [PATCH v1 1/4] clk: samsung: change COMMON_CLK_SAMSUNG default config logic Will McVicker
2021-09-21 7:29 ` Krzysztof Kozlowski
2021-09-21 7:50 ` Geert Uytterhoeven
2021-09-21 8:35 ` Krzysztof Kozlowski
2021-09-21 17:58 ` Will McVicker
2021-09-21 18:04 ` Krzysztof Kozlowski
2021-09-23 12:57 ` Lee Jones
2021-09-23 13:27 ` Krzysztof Kozlowski
2021-09-23 14:18 ` Lee Jones
2021-09-23 16:27 ` Krzysztof Kozlowski
2021-09-23 16:30 ` Krzysztof Kozlowski
2021-09-20 19:03 ` [PATCH v1 2/4] soc: samsung: change SOC_SAMSUNG " Will McVicker
2021-09-20 20:57 ` Will McVicker
2021-09-21 7:23 ` Krzysztof Kozlowski
2021-09-21 8:19 ` Lee Jones
2021-09-21 17:45 ` Will McVicker
2021-09-21 18:20 ` Krzysztof Kozlowski
2021-09-23 12:39 ` Lee Jones
2021-09-23 12:57 ` Krzysztof Kozlowski
2021-09-23 13:41 ` Lee Jones
2021-09-23 16:19 ` Geert Uytterhoeven
2021-09-23 18:05 ` Geert Uytterhoeven
2021-09-20 19:03 ` [PATCH v1 3/4] pinctrl: samsung: change PINCTRL_EXYNOS " Will McVicker
2021-09-21 7:27 ` Krzysztof Kozlowski
2021-09-21 8:18 ` Lee Jones
2021-09-23 21:52 ` Linus Walleij
2021-09-21 7:08 ` [PATCH v1 0/4] arm64: Kconfig: Update ARCH_EXYNOS select configs Lee Jones
2021-09-21 7:19 ` Krzysztof Kozlowski
2021-09-21 7:22 ` Krzysztof Kozlowski
2021-09-21 8:11 ` Lee Jones
2021-09-21 8:25 ` Krzysztof Kozlowski
2021-09-21 8:41 ` Lee Jones
2021-09-25 2:17 ` Saravana Kannan
2021-09-27 8:08 ` Krzysztof Kozlowski
2021-09-27 8:16 ` Geert Uytterhoeven [this message]
2021-09-27 18:07 ` Saravana Kannan
2021-09-27 19:54 ` Geert Uytterhoeven
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