linux-kernel - Re: [PATCH v3 -next 11/11] serial: 8250_early: Remove setup_early_serial8250

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Date:	Fri, 03 Apr 2015 14:27:30 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.cz>, Rob Herring <robh@...nel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v3 -next 11/11] serial: 8250_early: Remove setup_early_serial8250_console()

On 04/03/2015 01:44 PM, Yinghai Lu wrote:
> On Fri, Apr 3, 2015 at 10:38 AM, Peter Hurley <peter@...leysoftware.com> wrote:
>> On 04/03/2015 12:57 PM, Yinghai Lu wrote:
>>
>> Wait -- you have earlycon in a product??
> 
> What do you mean?

I mean, what will happen if I put in a big debug banner like Steven
did for ftrace?

Kernel developers need earlycon for debugging arch code; often the earlycon
is just hacked together especially when it requires fixmap support.

Putting it in a product and _relying on undocumented behavior_ is a bad idea.

> when you are using "console=uart8250,io,0x3f8"
> you will have earlycon at first, and handover to console.

which means you have to have CONFIG_SERIAL_EARLYCON to get a serial console
at all.

I have no problem fixing this _if this is causing actual regressions_,
and not simply some minor inconvenience that can be fixed by editing your
grub command line.

However, I see this undocumented behavior as a cautionary tale for why not
every kernel command line hack should be accepted in mainline.

Regards,
Peter Hurley
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