Re: Error in fbcon_switch ?

[Geert Uytterhoeven <geert@linux-m68k.org>]

On Tue, 20 May 2008, Krzysztof Helt wrote:
> I run into issue when two virtual consoles (tty1 and tty2) are set to different
> display modes: one with interlace and one without. When console is switched,
> the setting of the interlaced mode is not honoured, ie. 
> 
> tty1 (lace) -> tty2 (non-lace) -> tty1 (lace) -> tty2 (non-lace)
> 
> gives
> 
> tty1 (lace) -> tty2 (lace) -> tty1 (lace) -> tty2 (lace)
> 
> Of course, the refresh rate (and other timings) are not correct on the tty2 as
> the resolution and pixclock are preserved.

Interesting, I'll give it a try on my Amiga tonight...

> I found that root of the problem is that fbcon_switch copies the var.vmode 
> field from the previous console. If this copy is removed everything is alright, ie.
> 
> tty1 (lace) -> tty2 (non-lace) -> tty1 (lace) -> tty2 (non-lace)
> 
> Is this a correct solution to the problem? What is a purpose of copying vmode field?
> 
> The vmode field contains following settings:
> 
> #define FB_VMODE_INTERLACED     1       /* interlaced   */
> #define FB_VMODE_DOUBLE         2       /* double scan */
> #define FB_VMODE_ODD_FLD_FIRST  4       /* interlaced: top line first */
> #define FB_VMODE_MASK           255
> 
> #define FB_VMODE_YWRAP          256     /* ywrap instead of panning     */
> #define FB_VMODE_SMOOTH_XPAN    512     /* smooth xpan possible (internally used) */
> #define FB_VMODE_CONUPDATE      512     /* don't update x/yoffset       */
> 
> IMO, at least the first three should not be copied. I am not sure about YWRAP and 
> CONUPDATE/SMOOTH_XPAN.

As it copies [xy]offset, it probably needs YWRAP/SMOOTH_XPAN/CONUPDATE.
So I guess it should keep the bits under FB_VMODE_MASK.

> Regards,
> Krzysztof
> PS. The patch below is my fix:
> 
> diff -urp linux-old/drivers/video/console/fbcon.c linux-new/drivers/video/console/fbcon.c
> --- linux-old/drivers/video/console/fbcon.c	2008-05-12 19:27:04.305519626 +0200
> +++ linux-new/drivers/video/console/fbcon.c	2008-05-20 23:06:44.235878754 +0200
> @@ -2266,7 +2266,6 @@ static int fbcon_switch(struct vc_data *
>  	info->var.activate = var.activate;
>  	var.yoffset = info->var.yoffset;
>  	var.xoffset = info->var.xoffset;
> -	var.vmode = info->var.vmode;
>  	fb_set_var(info, &var);
>  	ops->var = info->var;

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

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