The background is complex: I did an implementation of a complete FPGA SOC with a MIPS32r1 core, they're all written by VerilogHDL, so technically it's an unique "soft-board". It's running happily without any problem, I promise!
Recently I'm trying to adapt a 5.2 Linux Kernel on it, and here the problem comes: The UART serial written is compatible with 8250/16550 model, and it successfully print "hello world", you know, on the U-Boot, which means the serial driver from U-Boot works really well. But when I was dealing with Linux-Kernel 5.2 later, I enabled early_con with '8250/16550 and compatible serial support' and early_printf with EXPERT set, but unfortunately they both didn't ever "say" something.
Next I tried to define a DT:
1 /dts-v1/;
2
3 #include "./xilfpga/microAptiv.dtsi"
4
5 / {
6 compatible = "generic";
7
8 aliases {
9 console = &uart_dev;
10 };
11
12 uart_dev: serial@bfe40000 {
13 compatible = "serial8250";
14 reg = <0xbfe40000 0x3fff>;
15 interrupts = <3 0>;
16 reg-shift = <0>;
17 clock-frequency = <66000000>;
18 };
19
20 };
and append it into vmlinux with below after I re-configured the kernel to support it.
mipsel-linux-gnu-objcopy --update-section .appended_dtb=arch/mips/boot/dts/cute.dtb
Although it's successfully compiled and appended, I still can't get any printed message when launching the kernel with cmdline below:
console=ttyS0,115200 initcall_debug=1 loglevel=20
or
earlycon console=ttyS0,115200 initcall_debug=1 loglevel=11
I expect the early message to be printed just like adapting the U-Boot after defined a DT, but it's not working. So I'm wondering if the early_con or early_printk needs an alternative board-level def or something else, or I'm doing bad... Much appreciated if you can provide any help!
