linux-kernel - Re: [PATCH 1/2] spi: dt-bindings: introduce linux,use-rt-queue flag

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Date:   Wed, 7 Jun 2023 15:21:43 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-spi@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux@...tq-group.com
Subject: Re: [PATCH 1/2] spi: dt-bindings: introduce linux,use-rt-queue flag

On Wed, Jun 07, 2023 at 02:55:31PM +0200, Matthias Schiffer wrote:

> It is not clear to me what alternative options we currently have if we
> want a setting to be effective from the very beginning, before
> userspace is running. Of course adding a cmdline option would work, but
> that seems worse than having it in the DT in every possible way.

Is it *really* that important that this be configured before userspace
is running?  With an initramfs you'd be able to do configuration before
even trying to mount filesystems if your primary storage is flash.  I'd
not expect the pre-userspace period to be under particular pressure
here.

Frankly I don't see the command line as being particularly worse here,
it's more tasteful and if you're doing some device specific
configuration it doesn't seem to make much difference.  Userspace looks
even better though.

> Requiring such tuning for specific drivers or driver instances is
> however a common issue for embedded systems, which is why we are seeing
> (and occasionally writing) such patches - setting things up from
> userspace may happen too late, or may not be possible at all if a
> setting needs to be available during probe. And even when deferring
> things to userspace is possible, making things configurable at runtime
> always adds some complexity, even though it is often not a requirement
> at all for embedded systems.

Using DT is all about adding complexity.

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