linux-kernel - Re: [PATCH] x86/earlyprintk: setup earlyprintk as early as possible

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Message-ID: <20150407102445.GA13658@gmail.com>
Date:	Tue, 7 Apr 2015 12:24:45 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Alexander Kuleshov <kuleshovmail@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/earlyprintk: setup earlyprintk as early as possible


* Alexander Kuleshov <kuleshovmail@...il.com> wrote:

> 2015-04-07 15:52 GMT+06:00 Ingo Molnar <mingo@...nel.org>:
> >
> > It would be nice to test it via a well placed printk() and check that
> > before the patch the message doesn't go to the serial console and
> > after the patch the message indeed arrives on the early serial console
> > - or something like that.
> 
> I have tested this patch when i wrote it and early_printk does not print
> anything before the parse_early_param. But i don't know how to show this
> in code in a correct way. [...]

Just add a debug printk() for your own testing, right after the param 
initialization call, to be confident that the early console indeed 
works.

> which i removed in the previous patch
> (https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=91d8f0416f3989e248d3a3d3efb821eda10a85d2)?
> 
> Any one another question about this. I submited patch only for 
> head64.c and it does not affect kernel for i386, because i'm not 
> sure where is the best place to setup earlyprintk in the head32.c. I 
> thought to put it in the start of i386_start_kernel(void) (from 
> head32.c) but not sure about it.

I'd use i386_start_kernel() on 32-bit and x86_64_start_kernel() on 
64-bit - but I haven't tested whether it actually works.

Thanks,

	Ingo
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