linux-kernel - [PATCH 4/7] arm64: dts: amlogic: gxl: enable UART RX and TX pull up by default

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Message-ID: <20250329185855.854186-5-martin.blumenstingl@googlemail.com>
Date: Sat, 29 Mar 2025 19:58:52 +0100
From: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To: linux-amlogic@...ts.infradead.org
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	jbrunet@...libre.com,
	khilman@...libre.com,
	neil.armstrong@...aro.org,
	christianshewitt@...il.com,
	Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: [PATCH 4/7] arm64: dts: amlogic: gxl: enable UART RX and TX pull up by default

Some boards have noise on the UART RX line when the UART pins are not
connected to another device (such as an USB UART adapter). This can
be addressed by using a pull up resistor. Not all boards may provide
such a pull up resistor on the PCB so enable the SoC's pull-up on the
UART RX and TX pads by default. This matches the default (from u-boot
or SoC hardware) state for the pinmux configuration on these pads.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
---
 arch/arm64/boot/dts/amlogic/meson-gxl.dtsi | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
index 2dc2fdaecf9f..460c46cfad6a 100644
--- a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
+++ b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
@@ -163,7 +163,7 @@ uart_ao_a_pins: uart_ao_a {
 			mux {
 				groups = "uart_tx_ao_a", "uart_rx_ao_a";
 				function = "uart_ao";
-				bias-disable;
+				bias-pull-up;
 			};
 		};
 
@@ -180,7 +180,7 @@ uart_ao_b_pins: uart_ao_b {
 			mux {
 				groups = "uart_tx_ao_b", "uart_rx_ao_b";
 				function = "uart_ao_b";
-				bias-disable;
+				bias-pull-up;
 			};
 		};
 
@@ -188,7 +188,7 @@ uart_ao_b_0_1_pins: uart_ao_b_0_1 {
 			mux {
 				groups = "uart_tx_ao_b_0", "uart_rx_ao_b_1";
 				function = "uart_ao_b";
-				bias-disable;
+				bias-pull-up;
 			};
 		};
 
@@ -522,7 +522,7 @@ mux {
 				groups = "uart_tx_a",
 				       "uart_rx_a";
 				function = "uart_a";
-				bias-disable;
+				bias-pull-up;
 			};
 		};
 
@@ -540,7 +540,7 @@ mux {
 				groups = "uart_tx_b",
 				       "uart_rx_b";
 				function = "uart_b";
-				bias-disable;
+				bias-pull-up;
 			};
 		};
 
@@ -558,7 +558,7 @@ mux {
 				groups = "uart_tx_c",
 				       "uart_rx_c";
 				function = "uart_c";
-				bias-disable;
+				bias-pull-up;
 			};
 		};
 
-- 
2.49.0