Can Protocol (small issue)

2026-01-29 18:13

Hi.
I have the luckfox lyra plus, and currenlty I am trying to work on an data intensive can application.
Going to the official documentation, I learned that in order to enable can I had to include the following snippet

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&can0 {
        assigned-clocks = <&cru CLK_CAN0>;
        assigned-clock-rates = <200000000>;
        pinctrl-names = "default";
        pinctrl-0 = <&rm_io30_can0_tx &rm_io31_can0_rx>;
        status = "okay";

};

in the device tree file kernel-6.1/arch/arm/boot/dts/rk3506g-luckfox-lyra-plus.dts
After rebuilding the kernel and the firmware without any issues and then flashing the board (SPI-NAND buildroot), this had as a result the following:

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root@luckfox:~# dmesg | grep -i can
[    1.502078] CAN device driver interface
[    1.503355] rk3576_canfd ff320000.can: Failed to request rxchan
[    1.503929] rk3576_canfd ff320000.can: CAN info: use_dma = 0, rx_max_data = 18, fifo_depth = 14
[    1.619928] can: controller area network core
[    1.620076] NET: Registered PF_CAN protocol family
[    1.620113] can: raw protocol
[    1.620140] can: broadcast manager protocol

Can was enabled but the rx side of the protocol was now Programmable IO (simply polling style) , this I suspect will limit the throughput.
After some thinking and slowly trying to understand .dts .dtsi notations (and learning that can0 is served by dmac0) I made this attempt:

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&can0 {
    assigned-clocks = <&cru CLK_CAN0>;
    assigned-clock-rates = <200000000>;
    pinctrl-names = "default";
    pinctrl-0 = <&rm_io30_can0_tx &rm_io31_can0_rx>;
    dmas = <&dmac0 20 1 0 0 0>; # channel request , direction[device --> mem] 
    dma-names = "rx";
    status = "okay";
};

But without any luck.
Has anybody faced this ?

2026-01-30 2:30

Hello, "rk3576_canfd ff320000.can: Failed to request rxchan" merely indicates that DMA is not being used for receiving. I'm not quite clear on what "Programmable IO (simply polling style)" refers to? RMIO mounts the pins to the CAN controller for receiving using interrupts rather than polling. Maybe this Programmable IO does not refer to RMIO.
The correct configuration of DMA in the device tree should be

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dmas = <&dmac0 0  0xff2880a8 0x000c0000 0x0 0x0>;
dma-names = "rx";

For details, please refer to https://opensource.rock-chips.com/image ... 250811.pdf. Finally, enter the system to view the logs.

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root@luckfox:~# dmesg | grep can
[    1.512608] rk3576_canfd ff320000.can: CAN info: use_dma = 1, rx_max_data = 18, fifo_depth = 14
[    1.636404] can: Controller Area Network core
[    1.636638] can: Raw protocol
[    1.636668] can: Broadcast Manager protocol
[    1.636701] can: Netlink gateway - max_hops=1
[    2.387587] ubi0: Scanning is finished

2026-02-01 1:57

Thank you for your reply.
After changing the .dts file the way you specified everything worked nicely!

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root@luckfox:~# dmesg | grep -i can
[    1.500689] CAN device driver interface
[    1.502588] rk3576_canfd ff320000.can: CAN info: use_dma = 1, rx_max_data = 18, fifo_depth = 14
[    1.619824] can: controller area network core
[    1.619986] NET: Registered PF_CAN protocol family
[    1.620024] can: raw protocol
[    1.620050] can: broadcast manager protocol
[    1.620078] can: netlink gateway - max_hops=1

Thank you!