linux-kernel - Re: [PATCH][RESEND] x86: Do not write to VGA memory space if CONFIG_VGA

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Date:	Mon, 19 Apr 2010 20:55:35 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Guenter Roeck <guenter.roeck@...csson.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"penberg@...helsinki.fi" <penberg@...helsinki.fi>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH][RESEND] x86: Do not write to VGA memory space if	CONFIG_VGA_CONSOLE
 is undefined

On 04/19/2010 07:21 PM, Guenter Roeck wrote:
> On Mon, Apr 19, 2010 at 05:02:25PM -0400, H. Peter Anvin wrote:
>> Hi Guenter,
>>
>> I wanted to check where we are at... at the very least we should drop
>> messages issued before initialization when isVGA != 1.
>>
>> Since serial ports require initialization, I really don't want to send
>> messages to the serial port before the port has been initialized, but
>> obviously it would be good to initialize earlyprintk as early as at all
>> possible.
>>
> Moving setup_early_printk() around may be possible, but I do not know
> the code good enough to take that risk. Even trying was a bad idea.
>
> I could submit a patch to add some protection into early_printk(),
> to ensure it does not write into VGA memory space if there is no VGA,
> and do that without changing current semantics - specifically, still
> write into VGA memory space even if setup_early_printk() was not called
> yet, but if boot_params.screen_info.orig_video_isVGA is set.
>
> I thought you indicated that you are opposed to changing the code,
> and it looks kind of clumsy, so I concluded that it was not worth
> trying again. Maybe I misunderstood - let me know.
>
> Guenter

I think writing into VGA memory if we know there is a VGA device is 
there.  I don't want to write to an uninitialized serial port, because 
that can cause all kinds of problems.

But yes, dropping output to VGA if there isn't one makes a lot of sense.

	-hpa
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