From: Rob Herring <robh+dt@kernel.org>
To: Wolfram Sang <wsa@kernel.org>,
linux-i2c@vger.kernel.org, devicetree-spec@vger.kernel.org,
Andi Shyti <andi.shyti@kernel.org>,
Rob Herring <robh+dt@kernel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
Chris Packham <chris.packham@alliedtelesis.co.nz>
Subject: Re: dtschema: i2c: messy situation about timeouts
Date: Mon, 26 Feb 2024 08:45:03 -0600 [thread overview]
Message-ID: <CAL_JsqKPofALm60XpexAVXj-cYZXyqo-eY0Z+Sx5q4QV0193hw@mail.gmail.com> (raw)
In-Reply-To: <ZdxjGwvGXlDGkYs0@shikoro>
On Mon, Feb 26, 2024 at 4:08 AM Wolfram Sang <wsa@kernel.org> wrote:
>
> Hey guys,
>
> we have quite a messy situation regarding I2C timeouts in the dtschema.
> Partly because I was too busy to pay detailed attention, partly because
> reviewing dtschema changes happen on Github which I totally missed. No
> complaining, though, here are my observations and suggestions to get it
> straight. Comments are more than welcome.
>
> - "i2c-transfer-timeout-us"
>
> Description says "Number of microseconds to wait before considering an
> I2C transfer has failed."
>
> To me, this binding is very descriptive and makes sense. We should keep
> it. Sadly, it is the newest one and we already have others.
>
>
> - "i2c-scl-has-clk-low-timeout"
>
> AFAIU this binding tells that the controller can do clock stretching.
> But what for? I don't see why this is important for clients. If
> anything, then it would be interesting if the *client* can do clock
> stretching and if the controller can actually handle that. But no need
> to describe it in DT, we have this as an adapter quirk already
> 'I2C_AQ_NO_CLK_STRETCH'. Two controllers use it, but no client checks
> for it so far. Coming back to this binding, it is also unused in the
> kernel.
>
> Suggestion: let's remove it
Seems like it can be implied by compatible... I'll defer to Andi.
>
>
> - "i2c-scl-clk-low-timeout-us"
>
> The description says "Number of microseconds the clock line needs to be
> pulled down in order to force a waiting state." What does "forcing a
> waiting state" mean here? I don't understand this description.
Does the commit msg or PR help?:
https://github.com/devicetree-org/dt-schema/pull/103
>
> It is used in the i2c-mpc driver. The use case is simply to put it into
> the 'struct i2c_adapter.timeout' member. That timeout is used to
> determine if a transfer failed. So, to me, "i2c-transfer-timeout-us"
> makes a lot more sense to use here.
>
> Suggestion: let's remove this binding and conver i2c-mpc to
> "i2c-transfer-timeout-us". Yes, not nice to have two deprecated
> bindings, but things happened.
Maybe the core code should read it instead?
I think we should mark as deprecated rather than remove unless we can
just remove the properties from the kernel. The reason being that
every property the kernel accesses should be documented. I might start
actually checking that. That's already done for compatible strings,
but those are mostly defined by a common pattern we can extract while
properties are less so.
Rob
next prev parent reply other threads:[~2024-02-26 14:45 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-26 10:08 dtschema: i2c: messy situation about timeouts Wolfram Sang
2024-02-26 14:45 ` Rob Herring [this message]
2024-02-26 21:16 ` Wolfram Sang
2024-02-26 20:20 ` Chris Packham
2024-02-26 21:24 ` Wolfram Sang
2024-02-27 0:03 ` Andi Shyti
2024-02-27 7:12 ` Wolfram Sang
2024-02-27 12:57 ` Wolfram Sang
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