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

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Date:   Thu, 7 Jan 2021 21:18:20 -0800
From:   Vineet Gupta <vgupta@...opsys.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        John Ogness <john.ogness@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Shreyas Joshi <shreyas.joshi@...mp.com>,
        shreyasjoshi15@...il.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org, buildroot@...ybox.net,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        linux-arch@...r.kernel.org,
        arcml <linux-snps-arc@...ts.infradead.org>
Subject: Re: ARC no console output (was Re: [PATCH 1/2] init/console: Use
 ttynull as a fallback when there is no console)

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@...opsys.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@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]#