linux-kernel - Re: [PATCH 2/3] dt-bindings: spi: Add DT schema for Tegra SPIDEV controller

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Message-ID: <9760cd70-cbd6-4865-92b9-b48eb2cdea55@sirena.org.uk>
Date: Thu, 27 Mar 2025 15:33:24 +0000
From: Mark Brown <broonie@...nel.org>
To: Jon Hunter <jonathanh@...dia.com>
Cc: Thierry Reding <thierry.reding@...il.com>, Vishwaroop A <va@...dia.com>,
	krzk+dt@...nel.org, robh@...nel.org, conor+dt@...nel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH 2/3] dt-bindings: spi: Add DT schema for Tegra SPIDEV
 controller

On Wed, Mar 26, 2025 at 12:16:53PM +0000, Jon Hunter wrote:
> On 25/03/2025 17:05, Mark Brown wrote:

> > > The way I imagine it, exporting would involve writing a chip-select to a
> > > specific SPI controller's "export" sysfs attribute to have a SPI device
> > > created for that particular chip-select and bind it to spidev.

> > My general feeling with those is that if you're building for them you're
> > probably either already modifiying your kernel or easily able to cope
> > with doing so.

> That's definitely what we do today, modify the kernel directly to achieve
> what we need. I am trying to avoid carrying too many out of tree patches for
> stuff like this and have something in the kernel that works by default. This
> is even more important for 3rd party Linux distros that will not accept
> non-upstream code.

Overlays should work well for that case too!

> Our devkits, very much like Raspberry PI, allow users to connect various
> hardware for development and so having an easy way to connect a SPI device
> is useful. For any production systems, users will definitely want a proper
> device and device-tree bindings. So I am just trying to explore what would
> be acceptable. If it is acceptable to have a sysfs interface for creating a
> SPI device at runtime, then we can look into that.

The main issue I see with the sysfs thing is that you have to describe
the presence of the device somehow which currently needs a device of
some kind there, it's not like I2C where you can just use the address.

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