[Buildroot] ARC no console output (was Re: [PATCH 1/2] init/console: Use ttynull as a fallback when there is no console)

[Vineet Gupta <vgupta@synopsys.com>]

On 1/7/21 7:48 PM, Sergey Senozhatsky wrote:
> On (21/01/07 09:58), Vineet Gupta wrote:
>> On 1/7/21 9:04 AM, Petr Mladek wrote:
>>> On Thu 2021-01-07 08:43:16, Vineet Gupta wrote:
>>>> Hi John,
>>>>
>>>> On 1/7/21 1:02 AM, John Ogness wrote:
>>>>> Hi Vineet,
>>>>>
>>>>> On 2021-01-06, Vineet Gupta <vgupta@synopsys.com> wrote:
>>>>>> This breaks ARC booting (no output on console).
>>>>>
>>>>> Could you provide the kernel boot arguments that you use? This series is
>>>>> partly about addressing users that have used boot arguments that are
>>>>> technically incorrect (even if had worked). Seeing the boot arguments of
>>>>> users that are not experiencing problems may help to reveal some of the
>>>>> unusual console usages until now.
>>>>
>>>>
>>>> Kernel command line: earlycon=uart8250,mmio32,0xf0005000,115200n8
>>>> console=ttyS0,115200n8 debug print-fatal-signals=1
>>>
>>> This is strange, the problematic patch should use ttynull
>>> only as a fallback. It should not be used when a particular console
>>> is defined on the command line.
>>
>> What happens in my case is console_on_rootfs() doesn't find /dev/console and
>> switching to ttynull. /dev is not present because devtmpfs doesn't automount
>> for initramfs.
> 
> I wonder if we'll move the nulltty fallback logic into printk code [1]
> will it fix the problem?
> 
> [1] https://lore.kernel.org/lkml/X6x%2FAxD1qanC6evJ at jagdpanzerIV.localdomain/

Your reasoning in the post above makes total sense.

I tired the patch: adding register_ttynull_console() call in 
console_device(), removing from console_on_rootfs() band that works too.


| Warning: unable to open an initial console. Fallback to ttynull.
| Warning: Failed to add ttynull console. No stdin, stdout, and stderr 
for the init process!
| Freeing unused kernel memory: 3096K
| This architecture does not have kernel memory protection.
| Run /init as init process
| with arguments:
|    /init
|  with environment:
|    HOME=/
|    TERM=linux
| Starting System logger (syslogd)
| Bringing up loopback device
| Starting inetd
| Mounting Posix Mqueue filesys
| 
CONFIG_INITRAMFS_SOURCE="~/arc/RAMFS/archs/ramfs_2011-GNU-2020-03-glibc-2.32-tiny"
| **********************************************************************
|			Welcome to ARCLinux
| **********************************************************************
| [ARCLinux]#