linux-kernel - Re: [PATCH v2 0/2] Fix regression introduced by disabling accelerated scrolling in fbcon

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Date:   Mon, 24 Jan 2022 23:41:22 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Helge Deller <deller@....de>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Pavel Machek <pavel@....cz>, Sam Ravnborg <sam@...nborg.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sven Schnelle <svens@...ckframe.org>,
        Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Claudio Suarez <cssk@...-c.es>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 0/2] Fix regression introduced by disabling
 accelerated scrolling in fbcon

On Mon, Jan 24, 2022 at 11:37:03PM +0100, Helge Deller wrote:
> On 1/24/22 23:19, Daniel Vetter wrote:
> > On Mon, Jan 24, 2022 at 10:03:17PM +0100, Helge Deller wrote:
> >> This series reverts two patches which disabled scrolling acceleration in
> >> fbcon/fbdev. Those patches introduced a regression for fbdev-supported graphic
> >> cards because of the performance penalty by doing screen scrolling by software
> >> instead of using existing 2D hardware acceleration.
> >>
> >> This series has been discussed on linux-fbdev, dri-devel and linux-kernel
> >> mailing lists. The consensus is that they will be reverted, but in addition
> >> it's being worked on to find a solution which allows to disable parts of the
> >> classic fbdev hardware acceleration code which isn't needed in DRM-only
> >> configurations.
> >
> > That's not my take at least.
> 
> Which is?
> Didn't we discussed about introducing something like
> CONFIG_FBCON_LEGACY_ACCELERATION ?

Yeah, as part of the reverts. Or at least that's what I meant to say.
-Daniel
> 
> >> The patchset is planned to be kept in fbdev's for-next git branch and later
> >> pushed into kernel v5.18 if no issues are found until then.
> >
> > Neither this. I don't think we've resovled maintainership of fbdev core
> > code and fbcon yet. That is the part that drm folks very much still
> > maintained, as a quick git shortlog will show.
> >
> > Maintaining these parts outside of drm trees just doesn't make sense,
> > since none of the other graphics relevant development happens outside of
> 
> I have no objections if you are willing to take those two patches through
> the drm tree.
> 
> Helge
> 
> >> ---
> >> Changes in v2 compared to v1:
> >> - adjusted the stable tags (one v5.10+, the other v5.16+)
> >> - moved the analysis and reasoning why those should be reverted into
> >>   the commit message. That simplifies to analyze later why they were
> >>   reverted.
> >> - resorted the To an Cc mail recipient lists
> >>
> >> Helge Deller (2):
> >>   Revert "fbdev: Garbage collect fbdev scrolling acceleration, part 1
> >>     (from TODO list)"
> >>   Revert "fbcon: Disable accelerated scrolling"
> >>
> >>  Documentation/gpu/todo.rst              |  24 --
> >>  drivers/video/fbdev/core/bitblit.c      |  16 +
> >>  drivers/video/fbdev/core/fbcon.c        | 540 +++++++++++++++++++++++-
> >>  drivers/video/fbdev/core/fbcon.h        |  59 +++
> >>  drivers/video/fbdev/core/fbcon_ccw.c    |  28 +-
> >>  drivers/video/fbdev/core/fbcon_cw.c     |  28 +-
> >>  drivers/video/fbdev/core/fbcon_rotate.h |   9 +
> >>  drivers/video/fbdev/core/fbcon_ud.c     |  37 +-
> >>  drivers/video/fbdev/core/tileblit.c     |  16 +
> >>  drivers/video/fbdev/skeletonfb.c        |  12 +-
> >>  include/linux/fb.h                      |   2 +-
> >>  11 files changed, 703 insertions(+), 68 deletions(-)
> >>
> >> --
> >> 2.31.1

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch