From: Wolfram Sang <wsa@kernel.org>
To: Chris Packham <Chris.Packham@alliedtelesis.co.nz>
Cc: "linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
"devicetree-spec@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>
Subject: Re: dtschema: i2c: messy situation about timeouts
Date: Mon, 26 Feb 2024 22:24:53 +0100 [thread overview]
Message-ID: <Zd0Bpa2ciMHmSQrS@shikoro> (raw)
In-Reply-To: <ccb58633-5981-4b91-a6ca-a57ea1ce5e40@alliedtelesis.co.nz>
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Hi Chris,
> > - "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'.
>
> Hmm I know of a few adapters that should probably set
> I2C_AQ_NO_CLK_STRETCH based on some Errata. Probably just a
That would be helpful if you could add that. I always guessed there
should be more controllers needing the flag but never encountered them
personally.
> documentation exercise. It would be nice to reject clients that need to
> do clock stretching but often it happens as a side effect rather than
> being intentional (I've seen this with i2c clients implemented in
> microcontrollers).
I guess the way forward with that is we add a flag like
I2C_CLIENT_CLK_STRETCH and let the core figure out if controller and
client are compatible. Dunno what to do if not, though. Reject? Throw a
warning that there might be problems? Probably reject by default unless
overridden by something-meaning-i-know-the-risks.
> > 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.
>
> Sounds like a good idea. We'd obviously need to keep support for the
> existing property but it wouldn't be hard to add
> "i2c-transfer-timeout-us". I'll try to whip up a patch for that sometime
> this week, just need to dust off my Freescale boards.
Please wait a little with the implementation. I want to try Rob's idea
to let the core set the timeout flag initially. Dusting off the boards
for testing would be awesome, though :)
Happy hacking,
Wolfram
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next prev parent reply other threads:[~2024-02-26 21:24 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
2024-02-26 21:16 ` Wolfram Sang
2024-02-26 20:20 ` Chris Packham
2024-02-26 21:24 ` Wolfram Sang [this message]
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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