From: Will McVicker <willmcvicker@google.com>
To: Olof Johansson <olof@lixom.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Saravana Kannan <saravanak@google.com>,
Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
Russell King <linux@armlinux.org.uk>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Michael Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@kernel.org>,
Sylwester Nawrocki <s.nawrocki@samsung.com>,
Tomasz Figa <tomasz.figa@gmail.com>,
Chanwoo Choi <cw00.choi@samsung.com>,
Linus Walleij <linus.walleij@linaro.org>,
Alessandro Zummo <a.zummo@towertech.it>,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
John Stultz <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Lee Jones <lee.jones@linaro.org>,
"Cc: Android Kernel" <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, Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v2 00/12] arm64: Kconfig: Update ARCH_EXYNOS select configs
Date: Fri, 1 Oct 2021 10:48:09 -0700 [thread overview]
Message-ID: <CABYd82ZHCrd5qhFUCTFPxPXn69LgdfWbW7zSMoTKaKq7FXvx=g@mail.gmail.com> (raw)
In-Reply-To: <CAOesGMiubqENbGSuQ_FQA59vA897R5nkgq5vu5Tg6kqbEVdz0A@mail.gmail.com>
On Fri, Oct 1, 2021 at 10:16 AM Olof Johansson <olof@lixom.net> wrote:
>
> On Fri, Oct 1, 2021 at 9:51 AM Will McVicker <willmcvicker@google.com> wrote:
> >
> > On Fri, Oct 1, 2021 at 9:00 AM Olof Johansson <olof@lixom.net> wrote:
> > >
> > > On Fri, Oct 1, 2021 at 4:59 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > >
> > > > Hi Olof,
> > > >
> > > > On Fri, Oct 1, 2021 at 7:36 AM Olof Johansson <olof@lixom.net> wrote:
> > > > > A much more valuable approach would be to work towards being able to
> > > > > free up memory by un-probed drivers at the end of boot. That would
> > > > > possibly benefit all platforms on all architectures.
> > > >
> > > > We used to have such a functionality in arch/ppc (not arch/powerpc!),
> > > > where code/data could be tagged __prep, __chrp, or __pmac, to put it
> > > > in a special section, and to be freed with initdata when unused. It
> > > > was removed in v2.6.15[1], as the savings weren't worth the hassle.
> > > > In a more fragmented space like arm the memory lost due to alignment
> > > > of the sections would be even more substantial.
> > >
> > > Yeah, the balance between per-platform code size and overall kernel
> > > code size shifted over time to a point where it wasn't as meaningful
> > > on ppc.
> > >
> > > > Another problem is to know when is the end of the boot, especially
> > > > with deferred probing.
> > >
> > > Most of this code either has a module_init() or an initcall that
> > > actually registers the drivers and/or probes for the platform and does
> > > the work.
> > >
> > > This means you can have a late equivalent hook/initcall that
> > > determines whether this path ended up being probed/used. If it wasn't,
> > > you can then unregister and flag the corresponding memory to be freed
> > > at the end, and would take out the heuristics and guessing on needing
> > > to do it automatically from the code path that's doing said freeing.
> > >
> > >
> > > -Olof
> >
> > First off, I appreciate the constructive conversations and I
> > understand the ask here. So I'd like to close the "we don't want this"
> > and "this isn't possible" conversation. We have already proven
> > downstream that it is in fact possible to modularize these drivers on
> > other SoCs (mentioned earlier if you missed it) and I'd like to direct
> > the conversation towards verifying/testing here instead of negatively
> > arguing about how SoC vendors aren't upstreaming their drivers. I
> > think everyone understands that, but unfortunately I have no control
> > over that even though I would love everyone to work upstream directly.
> >
> > I am fine with forcing these drivers to always be enabled in some form
> > upstream even though it doesn't really make much sense for a generic
> > kernel that will run on Qualcomm, Exynos, Mediatek, (you name it) SoC
> > devices. I thought about how to do this yesterday and wasn't able to
> > come up with a proper solution that didn't always force this driver to
> > be a module when CONFIG_MODULES is enabled.
>
> This line of reasoning: "I couldn't think of a better option" made us
> merge a userspace ABI some time ago that within a few months was
> replaced with a better solution. In that case it was the kernel
> headers bundling with a build (extending the vmlinux size by a lot),
> that seemed to have no concerns about binary growth. Not all that far
> after that went in, the BPF folks came up with a solid solution for
> CO-RE by introducing BTF, etc.
>
> So, the argument "I can't think of a better solution" is a local
> maxima that we shouldn't settle for if there's a likely better global
> maxima available with a bit more time/effort. If we say "this problem
> is worth solving but this doesn't seem to be the solution we want to
> go for" we might actually be better off long-term.
>
>
> -Olof
If the answer is, "we don't have a solution for that" then that's
fine. I'm not an expert at Kconfig configurations and am asking if
there is already a way to handle this. To me it sounded like there
might be a solution already due to this policy of "we don't allow
disabling drivers that are essential." I'll wait for Krysztof to
respond (or someone who has a potential solution) before I dig into
this deeper.
--Will
next prev parent reply other threads:[~2021-10-01 17:48 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-28 23:56 [PATCH v2 00/12] arm64: Kconfig: Update ARCH_EXYNOS select configs Will McVicker
2021-09-28 23:56 ` [PATCH v2 01/12] arm64: don't have ARCH_EXYNOS select EXYNOS_CHIPID Will McVicker
2021-09-29 13:58 ` (subset) " Krzysztof Kozlowski
2021-09-29 14:00 ` Krzysztof Kozlowski
2021-09-28 23:56 ` [PATCH v2 02/12] timekeeping: add API for getting timekeeping_suspended Will McVicker
2021-09-29 3:42 ` John Stultz
2021-09-29 20:01 ` Will McVicker
2021-09-29 20:46 ` John Stultz
2021-09-30 18:31 ` Will McVicker
2021-09-28 23:56 ` [PATCH v2 03/12] clk: samsung: add support for CPU clocks Will McVicker
2021-09-28 23:56 ` [PATCH v2 04/12] clk: samsung: exynos5433: update apollo and atlas clock probing Will McVicker
2021-09-28 23:56 ` [PATCH v2 05/12] clk: export __clk_lookup Will McVicker
2021-10-08 4:31 ` Stephen Boyd
2021-09-28 23:56 ` [PATCH v2 06/12] clk: samsung: modularize exynos arm64 clk drivers Will McVicker
2021-09-28 23:56 ` [PATCH v2 07/12] clk: samsung: set exynos arm64 clk driver as tristate Will McVicker
2021-09-29 13:09 ` Krzysztof Kozlowski
2021-09-28 23:56 ` [PATCH v2 08/12] pinctrl: samsung: modularize the ARM and ARM64 pinctrls Will McVicker
2021-09-29 2:01 ` Chanho Park
2021-09-28 23:56 ` [PATCH v2 09/12] pinctrl: samsung: set PINCTRL_EXYNOS and PINCTRL_SAMSUNG as tristate Will McVicker
2021-09-28 23:56 ` [PATCH v2 10/12] soc: samsung: pmu: modularize the Exynos ARMv8 PMU driver Will McVicker
2021-09-29 13:11 ` Krzysztof Kozlowski
2021-09-28 23:56 ` [PATCH v2 11/12] soc: samsung: pm_domains: modularize EXYNOS_PM_DOMAINS Will McVicker
2021-09-29 13:36 ` Krzysztof Kozlowski
2021-09-28 23:56 ` [PATCH v2 12/12] ARM: rtc: remove HAVE_S3C_RTC in favor of direct dependencies Will McVicker
2021-09-29 11:52 ` Alexandre Belloni
2021-09-29 13:02 ` [PATCH v2 00/12] arm64: Kconfig: Update ARCH_EXYNOS select configs Krzysztof Kozlowski
2021-09-29 19:48 ` Will McVicker
2021-09-30 6:14 ` Krzysztof Kozlowski
2021-09-30 9:01 ` Arnd Bergmann
2021-09-30 9:30 ` Lee Jones
2021-09-30 10:33 ` Krzysztof Kozlowski
2021-09-30 12:34 ` Lee Jones
2021-09-30 12:38 ` Krzysztof Kozlowski
2021-09-30 10:05 ` Geert Uytterhoeven
2021-09-30 9:23 ` Lee Jones
2021-09-30 10:17 ` Geert Uytterhoeven
2021-09-30 10:56 ` Lee Jones
2021-09-30 11:25 ` Geert Uytterhoeven
2021-09-30 12:08 ` Lee Jones
2021-09-30 16:09 ` Geert Uytterhoeven
2021-09-30 10:52 ` Krzysztof Kozlowski
2021-09-30 12:32 ` Lee Jones
2021-09-30 11:01 ` Tomasz Figa
2021-09-30 11:27 ` Geert Uytterhoeven
2021-09-30 11:51 ` Lee Jones
2021-09-30 12:10 ` Tomasz Figa
2021-09-30 12:15 ` Krzysztof Kozlowski
2021-09-30 12:45 ` Lee Jones
2021-10-01 4:01 ` Christoph Hellwig
2021-10-01 4:52 ` Saravana Kannan
2021-10-01 4:55 ` Christoph Hellwig
2021-09-30 12:21 ` Krzysztof Kozlowski
2021-09-30 12:39 ` Lee Jones
2021-09-30 13:08 ` Krzysztof Kozlowski
2021-09-30 13:29 ` Lee Jones
2021-09-30 16:12 ` Geert Uytterhoeven
2021-09-30 16:21 ` Lee Jones
2021-09-30 16:26 ` Geert Uytterhoeven
2021-09-30 18:02 ` Will McVicker
2021-10-01 4:04 ` Christoph Hellwig
2021-10-01 4:52 ` Olof Johansson
2021-10-01 5:23 ` Saravana Kannan
2021-10-01 5:35 ` Olof Johansson
2021-10-01 5:59 ` Will McVicker
2021-10-01 8:01 ` Krzysztof Kozlowski
2021-10-01 6:02 ` Saravana Kannan
2021-10-01 6:27 ` Olof Johansson
2021-10-01 6:30 ` Olof Johansson
2021-10-01 12:00 ` Arnd Bergmann
2021-10-01 12:31 ` Lee Jones
2021-10-01 15:43 ` Olof Johansson
2021-10-01 11:38 ` Linus Walleij
2021-10-01 11:59 ` Geert Uytterhoeven
2021-10-01 15:59 ` Olof Johansson
2021-10-01 16:51 ` Will McVicker
2021-10-01 17:15 ` Olof Johansson
2021-10-01 17:48 ` Will McVicker [this message]
2021-10-01 8:19 ` Geert Uytterhoeven
2021-10-01 9:00 ` Arnd Bergmann
2021-10-01 15:27 ` Olof Johansson
2021-10-01 19:26 ` Saravana Kannan
2021-10-02 1:47 ` Tomasz Figa
2021-10-02 21:03 ` Olof Johansson
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