linux-kernel - console vs earlycon ?

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Date:	Wed, 21 Oct 2015 17:21:07 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	linux-serial@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Cc:	Rob Herring <robh@...nel.org>, Stefan Agner <stefan@...er.ch>,
	Peter Hurley <peter@...leysoftware.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: console vs earlycon ?

Hi.

I think there are three places where console could be enabled.

[1] earlycon

Each driver entry is declared with
EARLYCON_DECLARE()  or OF_EARLYCON_DECLARE()

[2] console_init()

Each entry is declared with  console_initcall()

[3]  when driver is probed
The console is usually enabled at this point
unless some special treatment is done.

My question is about [2].

I am using 8250-ish UART device.

I noticed univ8250_console_match() and univ8250_console_setup()
always fail at the point of [2] unless early_serial_setup() has been
called in advance;
however, it looks like early_serial_setup() is only used for old platforms.

So, console cannot be enabled at [2] for modern platforms.

My questions are:

 -  Given that earlycon can be now available for major architectures such ARM,
     [2] will be deprecated at some point in the future?

 - I am implementing  earlycon  for my own UART driver.
   Is it meaningless to implement  console_initcall()  as well as earlycon?

-- 
Best Regards
Masahiro Yamada
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