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

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Message-ID: <YVWkxnc8wTdBgRsv@google.com>
Date:   Thu, 30 Sep 2021 12:51:34 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Tomasz Figa <tomasz.figa@...il.com>
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

On Thu, 30 Sep 2021, Tomasz Figa wrote:

> 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.

Is that the same as exporting symbols to framework APIs?

Since this is already a method GKI uses to allow external modules to
interact with the core kernel/frameworks.  However, it's not possible
to upstream these without an upstream user for each one.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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