linux-kernel - Re: [PATCH 01/13] dt-bindings: i2c: nomadik: add timeout-usecs property bindings

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Date: Wed, 21 Feb 2024 17:58:13 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: Théo Lebrun <theo.lebrun@...tlin.com>, "Linus Walleij"
 <linus.walleij@...aro.org>
Cc: "Rob Herring" <robh@...nel.org>, "Andi Shyti" <andi.shyti@...nel.org>,
 "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>, "Conor Dooley"
 <conor+dt@...nel.org>, "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 <linux-arm-kernel@...ts.infradead.org>, <linux-i2c@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-mips@...r.kernel.org>, "Gregory Clement"
 <gregory.clement@...tlin.com>, "Vladimir Kondratiev"
 <vladimir.kondratiev@...ileye.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>, "Tawfik Bayouk"
 <tawfik.bayouk@...ileye.com>
Subject: Re: [PATCH 01/13] dt-bindings: i2c: nomadik: add timeout-usecs
 property bindings

Hello,

On Mon Feb 19, 2024 at 3:29 PM CET, Théo Lebrun wrote:
> On Mon Feb 19, 2024 at 3:06 PM CET, Linus Walleij wrote:
> > On Fri, Feb 16, 2024 at 10:16 AM Théo Lebrun <theo.lebrun@...tlin.com> wrote:
> > > i2c-mpc (fsl,timeout) and i2c-gpio (i2c-gpio,timeout-ms). I agree this
> > > prop has no reason to be compatible-specific.
> > >
> > > Feedback from dt-bindings and I2C host maintainers would be useful: what
> > > should the property be named? Having the unit makes it self-descriptive,
> > > which sounds like a good idea to me. timeout-usecs, timeout-us, another
> > > option?
> >
> > Use i2c-transfer-timeout-ms in my opinion, so it us crystal clear
> > what that property is for.
>
> Using µs (microseconds) would be OK? I'm not sure yet about the exact
> timeout desired but a one millisecond granularity might not be enough
> for the Mobileye usecase.
>
> Expect incoming patches to use the I2C controller in Fast Mode Plus
> (1Mbps) and High Speed Mode (3.4Mbps). Gotta go fast!
>
> > As Rob mentioned this isn't in the kernel schemas but in dtschema, so
> > you need to patch this:
> > https://github.com/robherring/dt-schema
>
> Indeed. The other question if we do microseconds is the
> suffix: -us, -usecs, -microseconds, etc? I picked -usecs for my v1, but
> a grep tells me I am the only user of this suffix. -us is much more
> common.
>
> BTW i2c-controller.yaml already has a µs timeout:
> i2c-scl-clk-low-timeout-us

Note: I've sent a draft patch to dt-schema. See:
https://github.com/devicetree-org/dt-schema/pull/129

Feedback from I2C maintainers would confirm or infirm that this goes in
the right direction.

Thanks,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com