[SeaBIOS] [PATCH 2/2] vgabios: Limit the range of the VBE number of "pages" parameter.

[Kevin O'Connor]

On Sat, Sep 14, 2013 at 09:11:02AM +0200, Paul Menzel wrote:
> Am Freitag, den 13.09.2013, 16:24 -0400 schrieb Kevin O'Connor:
> > Looking at the output of other VGA BIOS implementations, it appears
> > that the number of available video pages reported is always between 1
> > and 127.
> 
> That is including 1 and 127, right?
> 
> > Signed-off-by: Kevin O'Connor <kevin at koconnor.net>
> > ---
> >  vgasrc/vbe.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/vgasrc/vbe.c b/vgasrc/vbe.c
> > index d962333..2c08736 100644
> > --- a/vgasrc/vbe.c
> > +++ b/vgasrc/vbe.c
> > @@ -144,6 +144,10 @@ vbe_104f01(struct bregs *regs)
> >              mode_attr |= VBE_MODE_ATTRIBUTE_LINEAR_FRAME_BUFFER_MODE;
> >          break;
> >      }
> > +    if (pages > 128)
> > +        pages = 128;
> 
> As 1 gets subtracted (below in diff), in this case 127 is included.
> 
> > +    if (pages < 2)
> > +        pages++;
> 
> Can pages be 0? If yes, it would be 0 again after substracting 1. Should
> it be `pages = 1` instead of `pages++`?

The goal was to report 0 if there isn't enough memory for even a
single image.  Ideally that would not happen in practice as it
shouldn't even be presented as a valid video mode if there isn't
enough memory for it.

Otherwise, the goal is to report between 1-127 (inclusive) for the
number of pages.  So, if there is only enough ram for 1 image, then
the code would report 1 (which means 2 images).  If there is enough
ram for more than 128 images, then the code would report 127 (which
means 128).  This is what the AMD VGABIOS appears to be doing.

-Kevin