[Buildroot] [help] configs/rock5b_defconfig: Switch to mainline kernel

["kilian.zinnecker--- via buildroot" <buildroot@buildroot.org>]

Hello,

The board support for the Rock5b uses a custom kernel. However, there already 
exists some mainline support for its SoC, the Rockchip RK3588 [1]. Some of it 
seems to already be present in kernel 6.6, which is the current latest version 
in buildroot. I would like to change the kernel used for the Rock5b from 
custom to mainline. Unfortunately I face a challenge.

In order to get kernel log output on the serial interface, I changed the 
consosole from ttyS2,1500000n8 to serial2,1500000n8 in the kernel bootargs (as 
seen in Sebastian Reichel's Kernel Recipes 2023 talk). After that, it shows 
the kernel messages, but it never reaches a shell:

[    0.321600] mmc_host mmc1: Bus speed (slot 0) = 400000Hz (slot req 
400000Hz, actual 400000HZ div = 0)
[    0.370827] hub 4-0:1.0: USB hub found
[    0.371218] hub 4-0:1.0: 1 port detected
[    0.372291] Waiting for root device /dev/mmcblk0p2...
[    0.382457] mmc_host mmc1: Bus speed (slot 0) = 198000000Hz (slot req 
200000000Hz, actual 198000000HZ div = 0)
[    0.497629] usb 1-1: new high-speed USB device number 2 using ehci-platform
[    0.655570] hub 1-1:1.0: USB hub found
[    0.656181] hub 1-1:1.0: 4 ports detected
[    0.794063] dwmmc_rockchip fe2c0000.mmc: Successfully tuned phase to 118
[    0.794672] mmc1: new ultra high speed SDR104 SDHC card at address 5048
[    0.796162] mmcblk1: mmc1:5048 SD32G 29.7 GiB
[    0.802500] GPT:Primary header thinks Alt. header is not at the end of the 
disk.
[    0.803155] GPT:563351 != 62357503
[    0.803459] GPT:Alternate GPT header not at the end of the disk.
[    0.803985] GPT:563351 != 62357503
[    0.804287] GPT: Use GNU Parted to correct GPT errors.
[    0.804761]  mmcblk1: p1 p2
[   31.717905] vdd_gpu_s0: disabling
[  115.285576] random: crng init done

Of course it could be, that it is just not configured anymore to put a shell on 
the serial interface, but I already tried to address that with:

BR2_TARGET_GENERIC_GETTY=y
BR2_TARGET_GENERIC_GETTY_PORT="serial2"

However, that did not seem to help. Could it be, that there is something wrong 
with the SD card formatting? It at least complains about it, but I am too 
unfamiliar with that, so I don't know whether it is a problem. I also tried to 
change the rootfs partition in the bootargs mmcblk0p2 to mmcblk1p2, but then 
the boot got stuck at some other place.

As kernel defconfig I use the default arm64 defconfig 
(BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG=y). Could that also be an issue, 
i.e., that I should provide a tailored one, e.g., by starting from the one 
used by the custom kernel?

I appreciate any help or suggestions, thanks and best regards,
Kilian

[1] https://gitlab.collabora.com/hardware-enablement/rockchip-3588/notes-for-rockchip-3588/-/blob/main/mainline-status.md


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