linux-kernel - Re: [PATCH v2 8/8] ARM: bcm2835: Disable i2c2 in the Device Tree

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Date:   Tue, 27 Sep 2016 19:25:48 +0200 (CEST)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     eric@...olt.net, wsa@...-dreams.de, swarren@...dotorg.org,
        Noralf Trønnes <noralf@...nnes.org>
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 8/8] ARM: bcm2835: Disable i2c2 in the Device Tree

> Noralf Trønnes <noralf@...nnes.org> hat am 27. September 2016 um 13:57
> geschrieben:
> 
> 
> i2c2 is connected to the HDMI connector and is controlled by the
> firmware. Disable it to stay out of harms way.

Until this point the commit message is okay, the rest is more confusing.

Btw this should avoid a warning about missing clock frequency.

> 
> From the downstream commit:
> i2c-bcm2708/BCM270X_DT: Add support for I2C2
> 
> The third I2C bus (I2C2) is normally reserved for HDMI use. Careless
> use of this bus can break an attached display - use with caution.
> 
> It is recommended to disable accesses by VideoCore by setting
> hdmi_ignore_edid=1 or hdmi_edid_file=1 in config.txt.
> 
> Signed-off-by: Noralf Trønnes <noralf@...nnes.org>
> ---
>  arch/arm/boot/dts/bcm2835-rpi.dtsi | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/arch/arm/boot/dts/bcm2835-rpi.dtsi
> b/arch/arm/boot/dts/bcm2835-rpi.dtsi
> index e9b47b2..8bffbee 100644
> --- a/arch/arm/boot/dts/bcm2835-rpi.dtsi
> +++ b/arch/arm/boot/dts/bcm2835-rpi.dtsi
> @@ -59,10 +59,6 @@
>  	clock-frequency = <100000>;
>  };
>  
> -&i2c2 {
> -	status = "okay";
> -};
> -

I'm not sure if this the right fix. According to bcm283x.dtsi the 3 i2c busses
have the same compatible string "brcm,bcm2835-i2c", but the changelog suggests
that this bus is "special".

Shouldn't we use a different compatible string? Our intention isn't to disable
i2c2 but avoid any claims of the usual i2c driver.

>  &sdhci {
>  	status = "okay";
>  	bus-width = <4>;
> -- 
> 2.8.2
> 
> 
> _______________________________________________
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> linux-arm-kernel@...ts.infradead.org
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