Linuxのデバイスツリーは難しいというお話。
Device Treeは謎が多い
RISC-Vエミュ でLinuxカーネルを動かすためにデバイスツリーを作成しているのですが、 UARTの割り込みIDがデバイスツリーで指定した値にならなくてハマりました。
問題がないデバイスツリーのファイルはgithubにコミットしているファイルで、以下の通りです。
正しい内容
/dts-v1/;
/ {
#address-cells = <2>;
#size-cells = <2>;
compatible = "riscv-virtio";
model = "RISCV Qemu Virtio";
chosen {
bootargs = "root=/dev/vda rw ttyS0";
stdout-path = "/uart@10000000";
};
uart@10000000 {
compatible = "ns16550a";
reg = <0x0 0x10000000 0x0 0x100>;
clock-frequency = <0x384000>;
interrupts = <10>;
interrupt-parent = <&intc>;
};
virtio_mmio@10001000 {
compatible = "virtio,mmio";
reg = <0x0 0x10001000 0x0 0x1000>;
interrupts = <1>;
interrupt-parent = <&intc>;
};
cpus {
#address-cells = <1>;
#size-cells = <0>;
timebase-frequency = <1000000>;
cpu@0 {
device_type = "cpu";
compatible = "riscv";
riscv,isa = "rv64abcdfimnsu";
mmu-type = "riscv,sv39";
reg = <0>;
clock-frequency = <0>;
status = "okay";
vic: interrupt-controller {
compatible = "riscv,cpu-intc";
#interrupt-cells = <1>;
interrupt-controller;
};
};
};
intc: intc@c000000 {
compatible = "riscv,plic0";
#interrupt-cells = <1>;
interrupt-controller;
reg = <0x0 0xc000000 0x0 0x4000000>;
interrupts-extended = <&vic 11 &vic 9>;
riscv,ndev = <0x35>;
};
memory@80000000 {
device_type = "memory";
reg = <0x0 0x80000000 0x0 0x8000000>;
};
clint@2000000 {
compatible = "riscv,clint0";
reg = <0x0 0x2000000 0x0 0x10000>;
interrupts-extended = <&vic 3 &vic 7>;
};
};
正しくない内容（割り込み番号が指定した値にならない）
上記を以下のように、uart@10000000とvirtio_mmio@10001000の位置をファイルの下の方に移動させると、
interruptsで指定した割り込み番号が設定値通りになりませんでした。
dtsのコンパイル時には何もワーニング等は何も出てきませんが、記述の順序にルールがあるのかなぁ。。
/dts-v1/;
/ {
#address-cells = <2>;
#size-cells = <2>;
compatible = "riscv-virtio";
model = "RISCV Qemu Virtio";
chosen {
bootargs = "root=/dev/vda rw ttyS0";
stdout-path = "/uart@10000000";
};
cpus {
#address-cells = <1>;
#size-cells = <0>;
timebase-frequency = <1000000>;
cpu@0 {
device_type = "cpu";
compatible = "riscv";
riscv,isa = "rv64abcdfimnsu";
mmu-type = "riscv,sv39";
reg = <0>;
clock-frequency = <0>;
status = "okay";
vic: interrupt-controller {
compatible = "riscv,cpu-intc";
#interrupt-cells = <1>;
interrupt-controller;
};
};
};
intc: intc@c000000 {
compatible = "riscv,plic0";
#interrupt-cells = <1>;
interrupt-controller;
reg = <0x0 0xc000000 0x0 0x4000000>;
interrupts-extended = <&vic 11 &vic 9>;
riscv,ndev = <0x35>;
};
memory@80000000 {
device_type = "memory";
reg = <0x0 0x80000000 0x0 0x8000000>;
};
clint@2000000 {
compatible = "riscv,clint0";
reg = <0x0 0x2000000 0x0 0x10000>;
interrupts-extended = <&vic 3 &vic 7>;
};
uart@10000000 {
compatible = "ns16550a";
reg = <0x0 0x10000000 0x0 0x100>;
clock-frequency = <0x384000>;
interrupts = <10>;
interrupt-parent = <&intc>;
};
virtio_mmio@10001000 {
compatible = "virtio,mmio";
reg = <0x0 0x10001000 0x0 0x1000>;
interrupts = <1>;
interrupt-parent = <&intc>;
};
};
まとめ
デバイスツリーの記述はよく分からん。