linux-kernel - Re: debug tip after earlycon is closed?

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Message-ID: <CAK7LNAQ7Ta18KrQnE2b_zZqW8xc_r9vRjQHzXnSF8ssuEy9QKA@mail.gmail.com>
Date:	Wed, 27 Jul 2016 12:26:27 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	Sebastian Reichel <sre@...nel.org>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>, linux-serial@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: debug tip after earlycon is closed?

Hi Sebastian,


2016-07-27 11:17 GMT+09:00 Sebastian Reichel <sre@...nel.org>:
> Hi,
>
> On Wed, Jul 27, 2016 at 10:23:09AM +0900, Masahiro Yamada wrote:
>> When the kernel fails to boot and its log console is silent,
>> I use earlycon and I often find the cause of error with it.
>>
>> But, I have been wondering if there is an easy-to-use
>> debug tip which is available after earlycon is disabled.
>>
>> I noticed the current mainline would not boot on my ARMv8 board.
>> According to the following log, I am guessing something wrong
>> is happening after the "bootconsole [uniphier0] disabled" log.
>>
>> Is there a good practice to see more log?
>
> Documentation/kernel-parameters.txt
>         keep_bootcon    [KNL]
>                         Do not unregister boot console at start. This is only
>                         useful for debugging when something happens in the window
>                         between unregistering the boot console and initializing
>                         the real console.


I did not know this kernel parameter, and it is exactly what I wanted.
Thanks a lot!


-- 
Best Regards
Masahiro Yamada