linux-kernel - Re: [PATCH v2 1/2] dt-bindings: i2c: add property to avoid device detection

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Date:   Sat, 14 May 2022 16:26:16 +0200
From:   Wolfram Sang <wsa@...nel.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     kernel@...s.com, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, krzk+dt@...nel.org, robh+dt@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: i2c: add property to avoid device
 detection

On Tue, Apr 12, 2022 at 10:50:45AM +0200, Vincent Whitchurch wrote:
> When drivers with ->detect callbacks are loaded, the I2C core does a
> bunch of transactions to try to probe for these devices, regardless of
> whether they are specified in the devicetree or not.  (This only happens
> on I2C controllers whose drivers enable the I2C_CLASS* flags, but this
> is the case for generic drivers like i2c-gpio.)
> 
> These kinds of transactions are unnecessary on systems where the
> devicetree specifies all the devices on the I2C bus, so add a property
> to indicate that the devicetree description of the hardware is complete
> and thus allow this discovery to be disabled.

Hmm, I don't think the name is fitting. "no-detect" is the desired
behaviour but a proper description is more like "bus-complete" or
something?

That aside, I am not sure we should handle this at DT level. Maybe we
should better change the GPIO driver to not populate a class if we have
a firmware node?


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