ARM: dts: amlogic: meson8: 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@googlemail.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20250329185855.854186-2-martin.blumenstingl@googlemail.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>

diff --git a/arch/arm/boot/dts/amlogic/meson8.dtsi b/arch/arm/boot/dts/amlogic/meson8.dtsi
index 847f7b1f1e9617cb8b7d153a1ae62b0ff2112606..7fe0c7d3ee6ec19dbde18dbb69cec3c800a7c0e7 100644 (file)
--- a/arch/arm/boot/dts/amlogic/meson8.dtsi
+++ b/arch/arm/boot/dts/amlogic/meson8.dtsi
@@ -398,7 +398,7 @@
                        mux {
                                groups = "uart_tx_ao_a", "uart_rx_ao_a";
                                function = "uart_ao";
-                               bias-disable;
+                               bias-pull-up;
                        };
                };
 
@@ -567,7 +567,7 @@
                                groups = "uart_tx_a1",
                                       "uart_rx_a1";
                                function = "uart_a";
-                               bias-disable;
+                               bias-pull-up;
                        };
                };