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From:   Tomasz Figa <tomasz.figa@gmail.com>
Date:   Thu, 30 Sep 2021 20:01:32 +0900
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Subject: Re: [PATCH v2 00/12] arm64: Kconfig: Update ARCH_EXYNOS select configs
To:     Lee Jones <lee.jones@linaro.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        Will McVicker <willmcvicker@google.com>,
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2021=E5=B9=B49=E6=9C=8830=E6=97=A5(=E6=9C=A8) 18:23 Lee Jones <lee.jones@li=
naro.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 hav=
e
> > 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