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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Message-ID: <t2o195c7a901004260843k947fdf2cy3b137e3056db8b62@mail.gmail.com>
Date:	Mon, 26 Apr 2010 17:43:44 +0200
From:	Bastien ROUCARIES <roucaries.bastien@...il.com>
To:	Guenter Roeck <guenter.roeck@...csson.com>
Cc:	linux-kernel@...r.kernel.org, penberg@...helsinki.fi,
	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

On Tue, Apr 20, 2010 at 6:16 PM, Guenter Roeck
<guenter.roeck@...csson.com> wrote:
> 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);
> +       }
>  }

Instead to this ugly if why not creating a null early_console (write
will do nothing) ?

>  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;
> +
>        return 0;
>  }

And assign null console as the last console as a fallback ?

Regards

Bastien
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