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Re: aarch64 grub serial output

From: Andrei Borzenkov
Subject: Re: aarch64 grub serial output
Date: Thu, 21 May 2020 21:25:08 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0

20.05.2020 18:29, Peter Geis пишет:
> Good Morning,
> I have an arm64 rk3399-rockpro64 that I am booting from u-boot to grub-efi.
> The boot path works fine, but I am unable to get the serial terminal working.

On EFI grub is using EFI Serial I/O Protocol. I do not see it
implemented by upstream U-Boot. Unless you are using custom U-Boot
version with serial io support I an afraid you are out of luck. Try
contacting U-Boot developers whether there are any plans to add serial

> I get the following output only:
> error: serial port `com2' isn't found.
> error: terminal `serial' isn't found.
> error: terminal `serial' isn't found.
> EFI stub: Booting Linux Kernel...
> EFI stub: EFI_RNG_PROTOCOL unavailable, no randomness supplied
> EFI stub: ERROR: Could not determine UEFI Secure Boot status.
> EFI stub: Using DTB from configuration table
> EFI stub: Exiting boot services and installing virtual address map...
> [    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd034]
> Here is my grub config, including the kernel command line showing a
> working serial output:
> GRUB_CMDLINE_LINUX_DEFAULT="earlycon=uart8250,mmio32,0xff1a0000
> console=tty0 console=ttyS2,1500000n8"
> GRUB_TERMINAL="console serial"
> GRUB_SERIAL_COMMAND="serial --speed=1500000 --unit=2 --word=8
> --parity=no --stop=1"

grub is using names to refer to serial ports, --unit=2 is simply
shorthand for "com2". Port names are platform dependent, "com2" is
recognized only on legacy BIOS. On EFI ports are names efi0, efi1, ...
in order firmware enumerates them. If firmware supports them of course
(see above).

> I see I the console errors on the serial connection passed from
> u-boot, but I can't figure out how to get a full console there.
> Any suggestions would be greatly appreciated.
> Thanks,
> Peter

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