Re: Grub2 UEFI boot and serial console output

[Andrei Borzenkov]

13.01.2017 19:40, Matwey V. Kornilov пишет:
> 2017-01-13 16:44 GMT+03:00 Andrei Borzenkov <address@hidden>:
>> 13.01.2017 12:03, Matwey V. Kornilov пишет:
>>> 2017-01-11 20:16 GMT+03:00 Andrei Borzenkov <address@hidden>:
>>>> 11.01.2017 19:55, Matwey V. Kornilov пишет:
>>>>> 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"?
>>>>
>>>> It is not.
>>>>
>>>>> Please correct me, if I am wrong.
>>>>>
>>>>
>>>> Again - "--unit=0" is simply alias for "com0". Whether device with name
>>>> "com0" actually exists depends on platform and loaded drivers.
>>>>
>>>> This alias makes no sense on platform that does not include ns8250
>>>> driver that provides access to device with name "com0". You can check
>>>> grub-core/Makefile.core.def which platforms include this driver.
>>>>
>>>> So on EFI you are not going to use --unit=0 (or you need to add some
>>>> platform-dependent magic to translate --unit=0 into platform device).
>>>>
>>>> And yes, this could use better documentation, both for "serial" command
>>>> and "Serial terminal" section.
>>>
>>> Thank you.
>>> "serial --speed=115200 efi0" also doesn't work.
>>
>> Please define "does not work". What you expect it to do and how you
>> verify it?
>>
> 
> I expect that it will show grub menu on serial port where I wait for
> it. I believe that the port itself is working because I see linux
> kernel console output redirected to serial after grub timeout.
> 
>>> It seems that there is no Serial IO protocol in my Insyde UEFI.
>>>

You can verify it by loading EFI Shell, and looking in devtree output
for something like "ISA Serial Port" or similar. You can also list all
handles with bound Serial IO protocol using

dh -p SerialIO


>>
>> What is output of "terminal_input" and "terminal_output"?
>>
>>
> 
> serial --speed=115200 efi0
> terminal_input serial
> terminal_output serial
> 

Well, it is messy indeed. First, I was wrong, and ns8250 driver is
compiled on EFI x86 platforms. Do you have x86 or ARM system?

Second, terminal names to use with "terminal_input" and
"terminal_output" are "serial_efi0" for port "efi0". Do you get any
error from the commands you listed?

Third, "serial" is alias to the first used ns8250 port. So

serial --unit=0
terminal_input serial

*will* work because the first command makes "serial" alias for
"serial_com0". But your commands will *not* work because they configure
port "efi0" but attempt to use port "com0" instead. May be we should
extend handling and make "serial" consistently to be alias for the first
used port, so the above sequence would work on each platform.

Finally I am not whether we should support direct hardware access with
ns8250 on EFI at all.

Here is what I get on x86 OVMF.


grub> lsmod
Name    Ref Count       Dependencies
minicmd 1
normal  1               gettext,boot,extcmd,bufio,crypto,terminal
gzio    0
gettext 2
extcmd  2
crypto  2
terminal        2
tar     1               archelp
archelp 2
memdisk 1
efinet  1               net
net     2               boot,datetime,bufio,priority_queue
priority_queue  3
bufio   5
datetime        3
boot    5
grub> terminal_input
Active input terminals:
console
Available input terminals:
serial_* serial at_keyboard
grub> serial --speed=115200 efi0
grub> lsmod
Name    Ref Count       Dependencies
serial  1               terminfo,extcmd
terminfo        2               extcmd
minicmd 1
normal  1               gettext,boot,extcmd,bufio,crypto,terminal
gzio    0
gettext 2
extcmd  7
crypto  2
terminal        2
tar     1               archelp
archelp 2
memdisk 1
efinet  1               net
net     2               boot,datetime,bufio,priority_queue
priority_queue  3
bufio   5
datetime        3
boot    5
grub> terminal_input
Active input terminals:
console
Available input terminals:
serial_efi0 serial_com0 serial at_keyboard
grub> terminal_output
Active output terminals:
console
Available output terminals:
serial_efi0 serial_com0 spkmodem serial gfxterm cbmemc audio
grub> serial --unit=0 --speed=115200
grub> serial --unit=1 --speed=115200
error: serial port `com1' isn't found.

Note, I am not sure whether use "serial_com0" will actually work, as it
obviously competes with EFI for hardware access so result may be
unpredictable.