linux-kernel - Re: [patch] early printk and boot console fixups.

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Message-Id: <200705161056.26386.bjorn.helgaas@hp.com>
Date:	Wed, 16 May 2007 10:56:26 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	"Gerd Hoffmann" <kraxel@...hat.com>, "Andi Kleen" <ak@...e.de>,
	akpm@...ux-foundation.org,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"linux kernel mailing list" <linux-kernel@...r.kernel.org>
Subject: Re: [patch] early printk and boot console fixups.

On Wednesday 16 May 2007 10:29:11 am Yinghai Lu wrote:
> On 5/16/07, Bjorn Helgaas <bjorn.helgaas@...com> wrote:
> > On Tuesday 15 May 2007 10:17:50 pm Yinghai Lu wrote:
> > > for early_uart_console, I have some ideas:
> > > 1. merged that into early_serial_console in
> > > arch/x86_64/kernel/early_printk.c, and
> > > move early_printk.c to kernel/, --- make it understand
> > >      earlyprintk=uart,io,0x3f8,9600n8
> > >      earlyprintk=uart,mmio,0xff5e0000,115200n8
> > > in addition to vga, ttyS, serial
> >
> > I would rather try to merge 8250_early and early_printk.
> > "console=uart,io,0x3f8" is already pretty similar to
> > "earlyprintk=serial", and it would be nice to have only one.
> >
> > "console=uart" does have the disadvantage that you have to know the
> > port address.  But it has the advantage that it doesn't depend on
> > compiled-in legacy serial port names.  If you need early console
> > output, you're probably a developer and can come up with the address.
> >
> > I think it would be nice to have a "console=vga".  That could use
> > the current "earlyprintk=vga" implementation, and automatically
> > hand off to tty0.
> >
> > Then we could remove "earlyprintk=" and always use "console=uart"
> > or "console=vga".
> 
> earlyprintk= is needed for seeting bootconsole, or setting CON_BOOT,
> and it is could be loaded earlier with early_param than console_init.

8250_early.c does basically the same thing as the serial part of
early_printk.c, so we should be able to make it work just as early.
I don't remember why I didn't use early_param() for 8250_early;
I probably should have.  On ia64, it doesn't matter because we call
early_serial_console_init() explicitly at about the time of
parse_early_param().

8250_early and early_printk are so similar, I just don't see the
need for both.

Bjorn
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