Re: [Linux-fbdev-devel] [PATCH 3/4] [ARM] s3c-fb: Add support for display panning

[Krzysztof H. <krz...@po...>]

On Thu, 9 Jul 2009 19:02:28 +0100
Russell King - ARM Linux <li...@ar...> wrote:

> On Thu, Jul 09, 2009 at 07:49:12PM +0200, Krzysztof Helt wrote:
> > On Thu, 09 Jul 2009 17:09:00 +0200
> > Pawel Osciak <p.o...@sa...> wrote:
> > > diff --git a/drivers/video/s3c-fb.c b/drivers/video/s3c-fb.c
> > > index ff0b1a3..77b77a2 100644
> > > --- a/drivers/video/s3c-fb.c
> > > +++ b/drivers/video/s3c-fb.c
> > > @@ -294,6 +294,8 @@ static int s3c_fb_set_par(struct fb_info *info)
> > >  	}
> > >  
> > >  	info->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8;
> > > +	info->fix.xpanstep = info->var.xres_virtual > info->var.xres ? 1 : 0;
> > > +	info->fix.ypanstep = info->var.yres_virtual > info->var.yres ? 1 : 0;
> > >  
> > 
> > These two lines are not need. If the xres_virtual > xres  there is no 
> > panning possible (the same is true for yres and yres_virtual).
> 
> Erm, I think you have that backwards.
> 

Right. The given conditions (xres_virtual < xres) are already checked by a 
higher layer so there is no need for this condition here.

> xres,yres is the visibly displayed dimentions.
> xres_virtual,yres_virtual is the size of the underlying framebuffer.
> 
> If the underlying framebuffer is larger than the visible display, you can
> pan the visible display around within the underlying framebuffer.
> 
> It is common for unaccelerated framebuffers used in text mode to have
> xres_virtual = xres, yres_virtual >> yres so that Y panning (or if your
> video driver supports it, wrapping) can occur to speed line scrolling.
> 

You are right, of course.

Regards,
Krzysztof

----------------------------------------------------------------------
Ubezpieczenie komunikacyjne wraz z ubezpieczeniem 
kosztow leczenia za granic±. http://link.interia.pl/f222b