linux-kernel - Re: console vs earlycon ?

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Message-ID: <5627E679.1050207@hurleysoftware.com>
Date:	Wed, 21 Oct 2015 15:24:41 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Stefan Agner <stefan@...er.ch>, linux-serial@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: console vs earlycon ?

On 10/21/2015 03:00 PM, Arnd Bergmann wrote:
> On Wednesday 21 October 2015 11:32:15 Peter Hurley wrote:
>> On 10/21/2015 10:13 AM, Arnd Bergmann wrote:
>>> On Wednesday 21 October 2015 09:53:47 Peter Hurley wrote:
>>>> I'm assuming the issue with trying to get console_init() working
>>>> is because the dummy color console causes the earlycon to be disabled?
>>>
>>> I don't think so.
>>>
>>> My line of thinking was more about usability: earlycon requires that
>>> you edit the kernel command line at the moment, while console_init()
>>> doesn't require any user interaction and just uses the stdout-path.
>>>
>>> I guess we could enable earlycon using a Kconfig symbol if we want
>>> to, or make it a per-architecture decision whether it's enabled even
>>> in the absence of the command line flag.
>>
>> Ah, I see. You want to start the stdout-path console at console_init()
>> time.
> 
> Yes, I see this as a tradeoff: we want the console to be as early as
> possible in order to report boot-time errors to the user, but not so early
> to require hacks that can cause problems themselves. earlycon has to
> do some scary stuff and is relatively recent, while the hacks
> necessary for console_init() are much older and better tested.

I assume you mean the hacks necessary to get _earlycon_ working at
console_init() time, because the hacks necessary to get non-8250
serial consoles working at console_init() would be extensive and
brand new.

Regards,
Peter Hurley
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