linux-kernel - Re: [PATCH v2] x86: Early-boot serial I/O support

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Message-ID: <4C38E5D8.30408@zytor.com>
Date:	Sat, 10 Jul 2010 14:27:52 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	Yinghai Lu <yinghai@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Cyrill Gorcunov <gorcunov@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2] x86: Early-boot serial I/O support

On 07/10/2010 02:17 PM, Pekka Enberg wrote:
> Hi!
> 
> On Sat, Jul 10, 2010 at 11:49 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>> can you analyze "console=uart8250,io,0x3f8,115200n8" instead?
>>
>> that is equal to "earlyprintk=ttyS0,115200 console=ttyS0,115200"
>>
>> so we only use one for all.
>>
>> also like to kill earlyprintk=ttyS0,115200 to favor earlycon
> 
> hpa, what's your take on this?
> 
> The 'console' variant seems overly complicated to me. We can add it
> but we also need to check for 'earlyprintk' as long as it's supported
> by the kernel.
> 

earlyprintk= seems to be preferred over console= these days.  Quite
frankly it's idiotic to have the user enter as many low-level details as
one has to do for the console= one.

Now, as for the I/O base, the I/O base for legacy serial ports are
available from a 4-element u16 array starting at absolute address 0x400.
 I don't think Linux currently examines that array -- instead relying on
the hard-coded values 0x3f8, 0x2f8, 0x3e8, 0x2e8 -- but it might
something to consider for the future.  However, we should match the
serial port subsystem there, of course.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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