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Independent BSP Repository

The Linux 5.15 independent BSP design separates Allwinner drivers and SoC configuration from the base kernel, reducing coupling between private drivers and a specific kernel version.

longan/
├── bsp/       # Allwinner drivers, Kconfig, Makefile, SoC DTSI, common config
├── device/    # board DTS, board defconfig, BoardConfig, partitions
└── kernel/    # standard Linux kernel code and interfaces

BSP Layout​

bsp/
├── configs/
├── drivers/
├── include/
├── Kconfig
├── Makefile
├── modules/
├── platform/
└── ramfs/

configs/ contains SoC-level DTSI and common defconfig files. drivers/ contains most Allwinner drivers. modules/ contains independently managed components such as NAND or GPU. include/ exports BSP headers.

Board Configuration​

Board-specific T527 files are usually below:

longan/device/config/chips/t527/configs/<BOARD>/

A branch may contain board.dts, linux-5.15/board.dts, bsp_defconfig, BoardConfig.mk, sys_config.fex, and sys_partition.fex.

After ./build.sh config, the kernel tree may contain a link such as:

longan/kernel/linux-5.15/bsp -> ../../bsp

Edit and commit the real files under longan/bsp/, not an assumed copied tree reached through the link.

defconfig Priority​

When files with the same name exist, the usual priority is:

board-level configuration
    >
SoC/default configuration
    >
BSP common configuration

Typical locations are:

longan/device/config/chips/t527/configs/<BOARD>/linux-5.15/bsp_defconfig
longan/device/config/chips/t527/configs/default/linux-5.15/bsp_defconfig
longan/bsp/configs/linux-5.15/*_defconfig

Some branches place the board defconfig directly under <BOARD>. Always verify with:

find longan/device/config/chips/t527 longan/bsp/configs/linux-5.15 \
    -type f -name '*defconfig' -print

Find a Driver Correctly​

cd <ANDROID_TOP>/longan

grep -Rni "config.*SUNXI.*UART\|SERIAL_SUNXI" bsp kernel device 2>/dev/null | head -50
find bsp kernel -type f \
    \( -iname '*uart*.c' -o -iname '*serial*.c' \) \
    -print

After locating it, identify the local Kconfig, Makefile, Device Tree compatible, and final CONFIG_ symbol.

Minimum Files for a New Driver​

bsp/drivers/<module>/
├── Kconfig
├── Makefile
├── <driver>.c
└── <driver>.h

Add the directory to its parent Kconfig and Makefile, then complete Device Tree, defconfig, build, and target verification.