Re: scrollmode selection problem

["Antonino A. Daplas" <adaplas@gmail.com>]

Knut Petersen wrote:
> Have a look at the following problem:
> 
> framebuffer memory size is 8MB
> xres is 800, yres is 600, bpp is 8.
> xres_virtual is 1024, yres_virtual is 8192.
> font dimensions 8x16
> 
> check_var() and set_par() are called, set_par() decides that ywrap
> scrolling is possible and sets FBINFO_HWACCEL_YWRAP.
> 
> Well, that decision is _wrong_  as  600/16 results in a 37 line display
> height, 8 pixel lines at the bottom are unused. But they are displayed,
> and obviously they contain garbage as YWRAP scrolling is selected by
> updatescrollmode().

I agree.

> 
> As the driver does know nothing about fonts, the obvious place to
> change is updatescrollmode().
> 
>        int good_wrap = (cap & FBINFO_HWACCEL_YWRAP) &&
>                divides(ywrap, vc->vc_font.height) &&
>                divides(vc->vc_font.height, vyres) &&
>                divides(vc->vc_font.height, yres);
> 
> would be a solution, but I don´t like it. There is no real reason that

It's a solution, and the correct one with the current code.

> ywrap
> scrolling should be disallowed when divides(vc->vc_font.height, vyres)
> or divides(vc->vc_font.height, yres) are false ... only limitations of the
> fbcon scrolling code.
> 
> Has someone already written code to remove that limitation?

None that I know of. Unfortunately, there's only a sprinkling of hardware
that supports ywrap, so you're the best bet to do that (hint, hint :-) 

Tony


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