linux-kernel - Re: [RFC/PATCH] x86: Early-boot serial I/O support

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Message-ID: <4C38C148.2060805@zytor.com>
Date:	Sat, 10 Jul 2010 11:51:52 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Cyrill Gorcunov <gorcunov@...il.com>
Subject: Re: [RFC/PATCH] x86: Early-boot serial I/O support

On 07/10/2010 11:07 AM, Pekka Enberg wrote:
> This patch adds serial I/O support to very early boot printf(). It's useful for
> debugging boot code when running Linux under KVM, for example. The actual code
> was lifted from early printk.

Yinghai is correct that this really needs to pick apart the command 
line, especially since there is already support for command-line parsing 
in the early boot code.  I suggest we just reuse the earlyprintk= 
option, especially since it's basically the same code and so should have 
the same failure profile.

> +
> +	while ((inb(early_serial_base + LSR)&  XMTRDY) == 0&&  --timeout)
> +		;
> +

cpu_relax(); here, probably.

	-hpa
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