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

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Date:   Tue, 6 Jun 2023 15:44:11 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        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 Tue, Jun 06, 2023 at 04:37:08PM +0200, Linus Walleij wrote:
> On Fri, Jun 2, 2023 at 2:22 PM Mark Brown <broonie@...nel.org> wrote:
> > On Fri, Jun 02, 2023 at 01:52:00PM +0200, Matthias Schiffer wrote:

> > > We have seen a number of downstream patches that allow enabling the
> > > realtime feature of the SPI subsystem to reduce latency. These were
> > > usually implemented for a specific SPI driver, even though the actual
> > > handling of the rt flag is happening in the generic SPI controller code.

> > > Introduce a generic linux,use-rt-queue flag that can be used with any
> > > controller driver. The now redundant driver-specific pl022,rt flag is
> > > marked as deprecated.

> > This is clearly OS specific tuning so out of scope for DT...

> In a sense, but to be fair anything prefixed linux,* is out of scope for DT,
> Documentation/devicetree/bindings/input/matrix-keymap.yaml being
> the most obvious offender.

That's at least a description of hardware though.  This is a performance
tuning thing, if it needs to be configured at all it should be
configured at runtime.  Some applications might see things work better,
some might see performance reduced and new versions might have different
performance characteristics and need different configuration.

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