From: Wolfram Sang <wsa@kernel.org>
To: Andi Shyti <andi.shyti@kernel.org>,
linux-i2c@vger.kernel.org, devicetree-spec@vger.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: Tue, 27 Feb 2024 13:57:52 +0100 [thread overview]
Message-ID: <Zd3cUKCHnn9n57pD@shikoro> (raw)
In-Reply-To: <Zd2LT-OM4KkUXCXn@ninjato>
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> > > - "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.
> >
> > It comes from the specification. The clock stretching is given as
> > an interval that can be tweaked depending on the hardware.
>
> You mean the maximum clock stretching is tweakable? That, in deed, could
> be a binding in the future, in theory. Yet, it would need support in the
> client drivers. Like a touchscreen driver which assumes a reset after a
> certain time of inactivity.
To sum it up: a binding defining the maximum time for clock stretching
makes sense in theory. I am currently not aware of a controller where
this could be used (but I surely don't know them all). Most of them keep
SCL low as long as they are busy internally. Not tweakable. So, we defer
this until there is a usecase.
If we ever add it, the above name of the binding cannot be used anymore
because i2c-mpc used it with a different purpose. Not so bad IMO because
"scl-clk" is a pleonasm anyway. I'd suggest "i2c-scl-max-stretch-us" but
am open for suggestions then.
This one can just be deprecated, I'd say.
Happy hacking!
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prev parent reply other threads:[~2024-02-27 12:57 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
2024-02-27 0:03 ` Andi Shyti
2024-02-27 7:12 ` Wolfram Sang
2024-02-27 12:57 ` Wolfram Sang [this message]
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