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Re: Grub2 UEFI boot and serial console output

From: Matwey V. Kornilov
Subject: Re: Grub2 UEFI boot and serial console output
Date: Wed, 11 Jan 2017 19:55:49 +0300

2017-01-11 19:45 GMT+03:00 Andrei Borzenkov <address@hidden>:
> 11.01.2017 16:27, Matwey V. Kornilov пишет:
>> Hello,
>> What is the proper way to output GRUB2 menu to serial rs232 console when
>> UEFI boot is used? I've copy-pasted GRUB_SERIAL_COMMAND="serial --unit=0
>> --speed=115200" from Google because I didn't find anything else. It
>> doesn't work.
>> Now, reading grub sources, I see that the proper way should probably be
>> something like GRUB_SERIAL_COMMAND="serial efi0".
> This is platform dependent. --unit=0 refers to COM1 on PC BIOS platform.
> On EFI grub is using EFI Serial I/O Protocol and enumerates all handles
> with this protocol using efiXX names. Then there is USB serial driver,
> ARC and IEEE1275 where names are provided by firmware etc.

I just can't understand, term/serial.c: grub_cmd_serial() sets name to
"com%ld" using --unit=value on any platform.

  if (state[OPTION_UNIT].set)
      grub_snprintf (pname, sizeof (pname), "com%ld",
                     grub_strtoul (state[0].arg, 0, 0));
      name = pname;

Then this "com0" is put to grub_serial_find(name) call. The question
is how this is going to match with "efi0"?
Please correct me, if I am wrong.

>> Could you please point me to proper documentation?
> You are welcome to contribute to it. Adding template section for
> platform dependent serial information and filling it with information
> known so far will be excellent - then other may extend it.

With best regards,
Matwey V. Kornilov

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