fbdev: Garbage collect fbdev scrolling acceleration

[Daniel Vetter]

On Thu, Jan 13, 2022 at 10:46:03PM +0100, Sven Schnelle wrote:
> Helge Deller <deller at gmx.de> writes:
> 
> > I may have missed some discussions, but I'm objecting against this patch:
> >
> > 	b3ec8cdf457e5 ("fbdev: Garbage collect fbdev scrolling acceleration, part 1 (from TODO list)")
> >
> > Can we please (partly) revert it and restore the scrolling behaviour,
> > where fbcon uses fb_copyarea() to copy the screen contents instead of
> > redrawing the whole screen?
> >
> > I'm fine with dropping the ypan-functionality.
> >
> > Maybe on fast new x86 boxes the performance difference isn't huge,
> > but for all old systems, or when emulated in qemu, this makes
> > a big difference.
> >
> > Helge
> 
> I second that. For most people, the framebuffer isn't important as
> they're mostly interested in getting to X11/wayland as fast as possible.
> But for systems like servers without X11 it's nice to have a fast
> console.

Fast console howto:
- shadow buffer in cached memory
- timer based upload of changed areas to the real framebuffer

This one is actually fast, instead of trying to use hw bltcopy and having
the most terrible fallback path if that's gone. Yes drm fbdev helpers has
this (but not enabled on most drivers because very, very few people care).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch