linux-kernel - Re: [PATCH] efi earlyprintk fix

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Date:	Mon, 4 Nov 2013 20:58:53 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	matt.fleming@...el.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efi earlyprintk fix

On 11/04/13 at 10:37am, Matt Fleming wrote:
> On Sun, 03 Nov, at 08:16:47PM, Dave Young wrote:
> > 
> > there's below one line shift problem:
> > 
> >                      ACPI=0xdabfe000  ACPI 2.0=0xdabfe014  SMBIOS=0xdaa9e000
> > [    0.000000] efi:  
> > 
> > In fact check efi_y and the lfb_height should be compared at the begin of the
> > loop of early_efi_write
>  
> Hmm... this is interesting. I can't produce this on any of my machines.
> Where did you see this? What hardware?

It's my laptop Thinkpad T420, the screen scolls very fast, I use boot_delay=500
to verify it with my patch for moving boot_delay param an early param.

Even without boot_delay, there's always a line at bottom with only the prefix:
"efi:"

> 
> > Signed-off-by: Dave Young <dyoung@...hat.com>
> > ---
> >  arch/x86/platform/efi/early_printk.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > --- linux-2.6.orig/arch/x86/platform/efi/early_printk.c
> > +++ linux-2.6/arch/x86/platform/efi/early_printk.c
> > @@ -106,6 +106,15 @@ early_efi_write(struct console *con, con
> >  		if (count > linemax)
> >  			count = linemax;
> >  
> > +		if (efi_y + font->height >= si->lfb_height) {
> > +			u32 i;
> > +
> > +			efi_y -= font->height;
> > +			early_efi_scroll_up();
> > +
> > +			for (i = 0; i < font->height; i++)
> > +				early_efi_clear_scanline(efi_y + i);
> > +		}
> >  		for (h = 0; h < font->height; h++) {
> >  			unsigned int n, x;
> >  
> > @@ -142,15 +151,6 @@ early_efi_write(struct console *con, con
> >  			efi_y += font->height;
> >  		}
> >  
> > -		if (efi_y + font->height >= si->lfb_height) {
> > -			u32 i;
> > -
> > -			efi_y -= font->height;
> > -			early_efi_scroll_up();
> > -
> > -			for (i = 0; i < font->height; i++)
> > -				early_efi_clear_scanline(efi_y + i);
> > -		}
> >  	}
> >  }
> 
> Notice how we figure out the initial value of efi_y...
> 
> static __init int early_efi_setup(struct console *con, char *options)
> {
> 	struct screen_info *si;
> 	u16 xres, yres;
> 	u32 i;
> 
> 	si = &boot_params.screen_info;
> 	xres = si->lfb_width;
> 	yres = si->lfb_height;
> 
> 	....
> 
> 	efi_y = rounddown(yres, font->height) - font->height;
> 
> Every time we enter early_efi_write(), we should have enough space to
> write one line, so I'm not at all sure what's going wrong with your
> display.
> 
> -- 
> Matt Fleming, Intel Open Source Technology Center
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