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 09:11:20 -0700
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	Bastien ROUCARIES <roucaries.bastien@...il.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 v3] x86: Do not write into VGA memory space if there is
	no  VGA device in the system

On Mon, Apr 26, 2010 at 11:43:44AM -0400, Bastien ROUCARIES wrote:
> 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 ?
> 
Sounds good to me. Peter, would that get your approval ?

Guenter
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