Re: scrollmode selection problem

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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