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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: Mon, 16 Jan 2017 12:57:47 +0300

2017-01-16 12:30 GMT+03:00 Andrei Borzenkov <address@hidden>:
> On Mon, Jan 16, 2017 at 12:25 PM, Matwey V. Kornilov
> <address@hidden> wrote:
>> 2017-01-16 12:22 GMT+03:00 Andrei Borzenkov <address@hidden>:
>>> On Mon, Jan 16, 2017 at 11:36 AM, Matwey V. Kornilov
>>> <address@hidden> wrote:
>>>>> I think here is my issue:
>>>>> terminal_input says that 'console' is active terminal and no other
>>>>> terminals available.
>>>>> serial --speed=115200 efi0 says "can't find command `serial'"
>>>> Ok, now I see! There is file /boot/grub2/x86_64-efi/serial.mod but
>>>> isnmod serial says that there is no such file.
>>> Well
>>> 1. $prefix must be set correctly (normally is done for you by
>>> grub-install & Co.; I do not know how you created your image)
>>> 2. Device which is part of $prefix must of course exist. You may need
>>> to explicitly load partition driver (not autoloaded) and/or virtual
>>> storage drivers (Linux MD, LVM2, LUKS, etc)
>>> 3. You need filesystem driver for this device (normally autoloaded).
>>> 4. Most vendors build images for use with Secure Boot that disable
>>> module load. Unless module is included in the image by vendor, it is
>>> flat unavailable. If you are using such image (you most likely do if
>>> you enabled secure boot support in your OS configuration) - check how
>>> image is built. You are using openSUSE, are not you?
>> Thank you. Yes, I am using openSUSE. And there is Secure Boot... All
>> this has been made by default installer.
> OK, I suggest that for testing you disable Secure Boot both in
> firmware setup and in YaST2. Then you will be using standard image
> generated by grub-install and will have access to all grub modules
> under $prefix. When you are sure serial port works for your setup,
> just submit SR to add serial to list of modules in signed grub image
> (see grub2.spec).

Now I see the menu on serial console. You are right about Secure Boot.
When Secure Boot is disabled, serial works as expected. However, efi
serial console is still not available in grub, but ns8250 is running

grub> terminal_input
Active input terminals:
Available input terminals:
console serial_com1 serial_com0 at_keyboard
grub> terminal_output
Active output terminals:
Available output terminals:
console serial_com1 serial_com0 spkmodem gfxterm cbmemc audio
grub> serial --speed=115200 efi0
error: serial port `efi0' isn't found.

With best regards,
Matwey V. Kornilov

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