linux-kernel - Re: [PATCH v2 00/12] arm64: Kconfig: Update ARCH

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Date:   Thu, 30 Sep 2021 20:01:32 +0900
From:   Tomasz Figa <tomasz.figa@...il.com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Will McVicker <willmcvicker@...gle.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Saravana Kannan <saravanak@...gle.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-rtc@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v2 00/12] arm64: Kconfig: Update ARCH_EXYNOS select configs

2021年9月30日(木) 18:23 Lee Jones <lee.jones@...aro.org>:
>
> I've taken the liberty of cherry-picking some of the points you have
> reiteratted a few times.  Hopefully I can help to address them
> adequently.
>
> On Thu, 30 Sep 2021, Krzysztof Kozlowski wrote:
> > Reminder: these are essential drivers and all Exynos platforms must have
> > them as built-in (at least till someone really tests this on multiple
> > setups).
>
> > Therefore I don't agree with calling it a "problem" that we select
> > *necessary* drivers for supported platforms. It's by design - supported
> > platforms should receive them without ability to remove.
>
> > The selected drivers are essential for supported platforms.
>
> SoC specific drivers are only essential/necessary/required in
> images designed to execute solely on a platform that requires them.
> For a kernel image which is designed to be generic i.e. one that has
> the ability to boot on vast array of platforms, the drivers simply
> have to be *available*.
>
> Forcing all H/W drivers that are only *potentially* utilised on *some*
> platforms as core binary built-ins doesn't make any technical sense.
> The two most important issues this causes are image size and a lack of
> configurability/flexibility relating to real-world application i.e.
> the one issue we already agreed upon; H/W or features that are too
> new (pre-release).
>
> Bloating a generic kernel with potentially hundreds of unnecessary
> drivers that will never be executed in the vast majority of instances
> doesn't achieve anything.  If we have a kernel image that has the
> ability to boot on 10's of architectures which have 10's of platforms
> each, that's a whole host of unused/wasted executable space.
>
> In order for vendors to work more closely with upstream, they need the
> ability to over-ride a *few* drivers to supplement them with some
> functionality which they believe provides them with a competitive edge
> (I think you called this "value-add" before) prior to the release of a
> device.  This is a requirement that cannot be worked around.

[Chiming in as a clock driver sub-maintainer and someone who spent a
non-insignificant part of his life on SoC driver bring-up - not as a
Google employee.]

I'd argue that the proper way for them to achieve it would be to
extend the upstream frameworks and/or existing drivers with
appropriate APIs to allow their downstream modules to plug into what's
already available upstream.

Best regards,
Tomasz