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UART / RS485 Configuration

1. Hardware confirmation​

Before editing, record the controller index, pinmux, voltage domain, supplies, reset/enable signals, interrupt, and external device model. For high-speed interfaces, also confirm topology, reference clock, and PHY sharing.

2. Locate the active platform configuration​

cd <ANDROID_TOP>/longan
find bsp device kernel -type f \( -name '*.dts' -o -name '*.dtsi' -o -name 'Kconfig' \)   | grep -Ei '<MODULE>|t527|sun55iw3'
grep -Rni '<compatible-or-config-keyword>' bsp device kernel

Do not assume that paths in a release guide exactly match the active branch, especially when moving from an older kernel to the Linux 5.15 independent BSP repository.

3. Kernel menuconfig​

./build.sh menuconfig

Check the following items:

  • CONFIG_AW_UART or CONFIG_AW_UART_NG (choose one, whichever is the platform)
  • CONFIG_AW_SERIAL_DMA（DMA）
  • CONFIG_DYNAMIC_DEBUG (dynamic debugging)
  • SERIAL_CORE / TTY

Save the configuration:

./build.sh saveconfig
# Verify which target defconfig changed
git diff -- device bsp

4. Device Tree example​

The following is a reference structure. Do not duplicate or override SoC-level reg, interrupts, clocks, or resets unless an erratum or an official patch requires it.

&uart7 {
        pinctrl-names = "default", "sleep";
        pinctrl-0 = <&uart7_pins_a>;
        pinctrl-1 = <&uart7_pins_b>;
        uart7_port = <7>;
        uart7_type = <4>;       /* Check the current driver for specific meaning. */
        status = "okay";
};

/* Software control RS485 The property name of the direction varies depending on the driver version. */
&uart7 {
        sunxi,uart-rs485 = <1>;
        sunxi,uart-485fl = <1>;
        sunxi,uart-485oe-gpios = <&pio PI 14 GPIO_ACTIVE_HIGH>;
};

5. Build and artifact validation​

./build.sh kernel 2>&1 | tee /tmp/module-kernel-build.log
./build.sh pack

Confirm that the configuration and node reached the final output:

grep -E '<CONFIG_KEY>' out/*/*/kernel/build/.config 2>/dev/null
find out -type f \( -name '*.dtb' -o -name '*.ko' \) | sort
dtc -I dtb -O dts -o /tmp/final.dts <FINAL_DTB>
grep -n -A30 -B5 '<NODE_OR_COMPATIBLE>' /tmp/final.dts

6. Change boundaries​

  • Keep SoC resources and common defaults in bsp/configs/linux-5.15/*.dtsi.
  • Keep board pins, supplies, reset, child devices, and status in the board board.dts.
  • Never edit generated build output or a mirrored symlink tree directly.
  • Evaluate shared changes against every product that includes the common DTSI.