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

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Date:	Wed, 31 Mar 2010 11:31:52 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Guenter Roeck <guenter.roeck@...csson.com>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com
Subject: Re: [PATCH][RESEND] x86: Do not write to VGA memory space if CONFIG_VGA_CONSOLE
 is undefined

On 03/31/2010 07:41 AM, Guenter Roeck wrote:
> Current early_printk code writes into VGA memory space even
> if CONFIG_VGA_CONSOLE is undefined. This can cause problems
> if there is no VGA device in the system, especially if the memory
> is used by another device.
> 
> Fix problem by redirecting output to early_serial_console
> if CONFIG_VGA_CONSOLE is undefined.
> 
> Signed-off-by: Guenter Roeck <guenter.roeck@...csson.com>
>  
>  asmlinkage void early_printk(const char *fmt, ...)
> @@ -216,7 +224,7 @@ static int __init setup_early_printk(char *buf)
>  			early_serial_init(buf + 4);
>  			early_console_register(&early_serial_console, keep);
>  		}
> -		if (!strncmp(buf, "vga", 3) &&
> +		if (have_vga_console && !strncmp(buf, "vga", 3) &&
>  		    boot_params.screen_info.orig_video_isVGA == 1) {
>  			max_xpos = boot_params.screen_info.orig_video_cols;
>  			max_ypos = boot_params.screen_info.orig_video_lines;

I'm confused in a big way about how you could end up with a system where:

a) there is no VGA;
b) VGA memory is used by another device(!!!);
c) boot_params.screen_info.orig_video_isVGA == 1?

	-hpa
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