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

From: Alexander Stein <alexander.stein@ew.tq-group.com>
To: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>,
	linux-arm-kernel@lists.infradead.org
Cc: Mark Brown <broonie@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	linux-spi@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux@ew.tq-group.com,
	Linus Walleij <linus.walleij@linaro.org>
Subject: Re: [PATCH 1/2] spi: dt-bindings: introduce linux,use-rt-queue flag
Date: Fri, 09 Jun 2023 10:15:37 +0200	[thread overview]
Message-ID: <3241150.44csPzL39Z@steina-w> (raw)
In-Reply-To: <CACRpkdb=2fogk3bEa4fkPVYQivnvLh1F1TnBj7og43ak+F8gPw@mail.gmail.com>

Hi all,

Am Freitag, 9. Juni 2023, 09:41:14 CEST schrieb Linus Walleij:
> On Wed, Jun 7, 2023 at 2:55 PM Matthias Schiffer
> 
> <matthias.schiffer@ew.tq-group.com> 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.
> 
> A agree with Mark that a command line option isn't that bad. It's something
> that pertains to just the Linux kernel after all? And you can put that
> command line option in the default device tree, in chosen, if you want.

I don't like the idea of a command line enabling realtime scheduling for all 
instances of the SPI controller driver or even all SPI controllers. Actually 
this might be worse if a non-rt SPI bus is considered for RT scheduling.
IMHO this should be configurable per SPI controller, e.g. a sysfs attribute.

> No-one is going to
> complain about that.

IIRC someone (maybe Greg K-H) opposed pretty hard against (module) parameters 
for (driver) configuration, but I can't find the post to back my statement.

Best regards,
Alexander

> Yours,
> Linus Walleij
> 
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