linux-kernel - Re: [PATCH v3] x86: Do not write into VGA memory space if there is no VGA device in the system

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Date:	Mon, 26 Apr 2010 12:36:05 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Guenter Roeck <guenter.roeck@...csson.com>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com, x86@...nel.org
Subject: Re: [PATCH v3] x86: Do not write into VGA memory space if there is
 no VGA device in the system

Guenter Roeck kirjoitti:
> Ensure that early_printk() does not write into VGA memory space
> if there is not VGA device in the system.
> 
> Signed-off-by: Guenter Roeck <guenter.roeck@...csson.com>
> ---
> v3:
> Changes are now limited to early_printk.c. Functionality is retained, meaning
> there will still be output on the VGA console before setup_early_printk()
> is called, but only if a VGA device is known to exist in the system.
> 
>  arch/x86/kernel/early_printk.c |   17 +++++++++++++----
>  1 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
> index b9c830c..783cb25 100644
> --- a/arch/x86/kernel/early_printk.c
> +++ b/arch/x86/kernel/early_printk.c
> @@ -170,10 +170,13 @@ asmlinkage void early_printk(const char *fmt, ...)
>  	int n;
>  	va_list ap;
>  
> -	va_start(ap, fmt);
> -	n = vscnprintf(buf, sizeof(buf), fmt, ap);
> -	early_console->write(early_console, buf, n);
> -	va_end(ap);
> +	if (early_console && (early_console_initialized ||
> +			      boot_params.screen_info.orig_video_isVGA == 1)) {
> +		va_start(ap, fmt);
> +		n = vscnprintf(buf, sizeof(buf), fmt, ap);
> +		early_console->write(early_console, buf, n);
> +		va_end(ap);
> +	}
>  }
>  
>  static inline void early_console_register(struct console *con, int keep_early)
> @@ -233,6 +236,12 @@ static int __init setup_early_printk(char *buf)
>  #endif
>  		buf++;
>  	}
> +
> +	/* If there is no VGA device, don't try to use it as early console. */
> +	if (early_console == &early_vga_console &&
> +	    boot_params.screen_info.orig_video_isVGA != 1)
> +		early_console = NULL;

Wouldn't it be better to switch to, say, serial console here to avoid 
the NULL check in early_printk()?

> +
>  	return 0;
>  }
> 
--
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