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Linux Drivers and Projects

Driver Integration Layout​

A new driver commonly contains:

drivers/vendor/mydevice/
├── Kconfig
├── Makefile
└── mydevice.c

The parent Kconfig and Makefile must include the directory. A driver can be built in with =y or built as a module with =m.

Device-tree Matching​

mydevice@10000000 {
    compatible = "vendor,mydevice";
    reg = <0x0 0x10000000 0x0 0x1000>;
    interrupts = <...>;
    clocks = <&ccu ...>;
    resets = <&ccu ...>;
    pinctrl-names = "default";
    pinctrl-0 = <&mydevice_pins>;
    status = "okay";
};

The driver matches compatible through of_match_table and obtains registers, interrupts, clocks, resets, GPIOs, and regulators in probe().

User-space Interfaces​

  • /dev: stable read/write/ioctl/poll interface.
  • sysfs: small attributes and state.
  • debugfs: development debugging, not a stable ABI.
  • procfs: legacy compatibility; prefer sysfs/debugfs for new interfaces.
  • netlink: event delivery and control messages.

GPIO LED Application​

New kernels favor the GPIO character device and libgpiod. If the current SDK still enables sysfs GPIO, a temporary test is:

echo 102 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio102/direction
echo 1 > /sys/class/gpio/gpio102/value

GPIO 102 is only an example. Confirm the actual LED pin from the X821 schematic and device tree.

Cross-build Makefile:

CROSS_COMPILE ?= riscv64-unknown-linux-gnu-
CC := $(CROSS_COMPILE)gcc
CFLAGS := -Wall -O2

all: gpio_led_demo

gpio_led_demo: src/gpio_led_demo.c
	$(CC) $(CFLAGS) -o $@ $<

clean:
	rm -f gpio_led_demo

System-monitor Daemon​

A daemon can periodically read:

/proc/stat
/proc/meminfo
/proc/uptime
/sys/class/thermal/

Include log rotation, signal-based shutdown, configuration validation, watchdog heartbeat, and write-rate limiting. Storage is limited on the V821; logs must not grow without bounds.

SDK Integration​

Package the application as an OpenWrt package, install the binary under /usr/bin, configuration under /etc, and the init script under /etc/init.d. This integrates menuconfig, dependencies, rootfs packaging, and version control.