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 09:58:05 -0800
From:   Vineet Gupta <vgupta@...opsys.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        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 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.

> The only explanation would be that ttyS0 gets registered too late
> and ttynull is added as a fallback in the meantime.

I don't know if ttyS0 console should have registered already but even if 
it did - the /dev node missing would not have helped ?

> 
> Anyway, I propose the revert the problematic patch for 5.11-rc3,
> see
> https://lore.kernel.org/lkml/20210107164400.17904-2-pmladek@suse.com/
> This mystery is a good reason to avoid bigger changes at this stage.
> 
> Best Regards,
> Petr
>