linux-kernel - Re: [PATCH 1/2] i2c: add binding to prevent device detection

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Date:   Tue, 5 Apr 2022 15:57:16 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>, wsa@...nel.org
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 1/2] i2c: add binding to prevent device detection

On 05/04/2022 14:16, 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.)
> 

Thank you for your patch. There is something to discuss/improve.

> These kinds of transactions are unnecessary on systems where the
> devicetree specifies all the devices on the I2C bus, so add a property
> to allow them to be disabled.
> 
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
> ---
>  Documentation/devicetree/bindings/i2c/i2c.txt | 4 ++++

Use the subject matching the subsystem (git log --oneline -- .......).

>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> index fc3dd7ec0445..5f7bdf4851e8 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> @@ -72,6 +72,10 @@ wants to support one of the below features, it should adapt these bindings.
>  	this information to adapt power management to keep the arbitration awake
>  	all the time, for example. Can not be combined with 'single-master'.
>  
> +- no-detect
> +	states that the system should not attempt to automatically detect
> +	devices which are not explicitly specified as child nodes.

Focus on the hardware, not on system and behavior. The hardware property
is that bus is completely described in Devicetree or detection does not
work correctly. I guess the property name could stay like this, but the
description could be rephrased.

Best regards,
Krzysztof