linux-kernel - Re: [PATCH] arm64: dts: amlogic: gxl: set i2c bias to pull-up

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Message-ID: <20523c9e-f7de-4355-82ed-380ee03083f0@linaro.org>
Date: Mon, 28 Apr 2025 09:32:07 +0200
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Da Xue <da@...re.computer>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Kevin Hilman <khilman@...libre.com>,
 Jerome Brunet <jbrunet@...libre.com>,
 Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc: devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: amlogic: gxl: set i2c bias to pull-up

On 25/04/2025 22:31, Da Xue wrote:
> GXL I2C pins need internal pull-up enabled to operate if there
> is no external resistor. The pull-up is 60kohms per the datasheet.
> 
> We should set the bias when i2c pinmux is enabled.

So, yes in some cases when the on-board pull-up is missing, the on-pad
pull-up is required, but the whole idea was to only add the pull-up property
when needed.

So I know the real motivation is again about the 40pin headers, where
some applications don't add a pull-up and still want to have i2c working.

So my question is: why can't the pull-up property be added in overlays ?

Neil

> 
> Signed-off-by: Da Xue <da@...re.computer>
> ---
>   arch/arm64/boot/dts/amlogic/meson-gxl.dtsi | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
> index 2dc2fdaecf9f..aed8dbfbb64d 100644
> --- a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
> +++ b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
> @@ -214,7 +214,7 @@ mux {
>   				groups = "i2c_sck_ao",
>   				       "i2c_sda_ao";
>   				function = "i2c_ao";
> -				bias-disable;
> +				bias-pull-up;
>   			};
>   		};
>   
> @@ -576,7 +576,7 @@ mux {
>   				groups = "i2c_sck_a",
>   				     "i2c_sda_a";
>   				function = "i2c_a";
> -				bias-disable;
> +				bias-pull-up;
>   			};
>   		};
>   
> @@ -585,7 +585,7 @@ mux {
>   				groups = "i2c_sck_b",
>   				      "i2c_sda_b";
>   				function = "i2c_b";
> -				bias-disable;
> +				bias-pull-up;
>   			};
>   		};
>   
> @@ -594,7 +594,7 @@ mux {
>   				groups = "i2c_sck_c",
>   				      "i2c_sda_c";
>   				function = "i2c_c";
> -				bias-disable;
> +				bias-pull-up;
>   			};
>   		};
>   
> @@ -603,7 +603,7 @@ mux {
>   				groups = "i2c_sck_c_dv19",
>   				      "i2c_sda_c_dv18";
>   				function = "i2c_c";
> -				bias-disable;
> +				bias-pull-up;
>   			};
>   		};
>