Re: [Qemu-devel] [PATCH 4/9] fbdev: add linux framebuffer display driver.

[Stefano Stabellini]

On Fri, 21 Sep 2012, Gerd Hoffmann wrote:
>   Hi,
> 
> >> +    case FB_ACQ_REQ:
> >> +        fbdev_switch_acquire();
> >> +        redraw_screen++;
> > 
> > Rather than introducing redraw_screen, I would just call vga_hw_invalidate
> > instead here. It is always a win if we can avoid to introduce one more
> > state machine.
> 
> Wouldn't that make the vga emulation do additional work which is simply
> not needed?

It causes full_update to be set and that causes vga_draw_line to be
called for every line on the screen.
However in the important cases (32bpp and 16bpp) the buffer is shared
and nothing happens. So no more work.