linux-kernel - Re: [PATCH 03/21] fbcon: Restore fbcon scrolling acceleration

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Date:   Tue, 1 Feb 2022 14:45:16 +0100
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     Helge Deller <deller@....de>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        linux-fbdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, Claudio Suarez <cssk@...-c.es>,
        Dave Airlie <airlied@...il.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Pavel Machek <pavel@....cz>, Sam Ravnborg <sam@...nborg.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Sven Schnelle <svens@...ckframe.org>,
        Gerd Hoffmann <kraxel@...hat.com>
Subject: Re: [PATCH 03/21] fbcon: Restore fbcon scrolling acceleration

On Tue, Feb 1, 2022 at 12:01 PM Helge Deller <deller@....de> wrote:
> On 2/1/22 11:36, Daniel Vetter wrote:
> > On Tue, Feb 1, 2022 at 11:16 AM Helge Deller <deller@....de> wrote:
> >>
> >> On 1/31/22 22:05, Daniel Vetter wrote:
> >>> This functionally undoes 39aead8373b3 ("fbcon: Disable accelerated
> >>> scrolling"), but behind the FRAMEBUFFER_CONSOLE_LEGACY_ACCELERATION
> >>> option.
> >>
> >> you have two trivial copy-n-paste errors in this patch which still prevent the
> >> console acceleration.
> >
> > Duh :-(
> >
> > But before we dig into details I think the big picture would be
> > better. I honestly don't like the #ifdef pile here that much.
>
> Me neither.
> The ifdefs give a better separation, but prevents that the compiler
> checks the various paths when building.
>
> > I wonder whether your approach, also with GETVX/YRES adjusted
> > somehow, wouldn't look cleaner?
> I think so.
> You wouldn't even need to touch GETVX/YRES because the compiler
> will optimize/reduce it from
>
> #define GETVYRES(s,i) ({                           \
>         (s == SCROLL_REDRAW || s == SCROLL_MOVE) ? \
>         (i)->var.yres : (i)->var.yres_virtual; })
>
> to just become:
>
> #define GETVYRES(s,i) ((i)->var.yres)

Yeah, but you need to roll out your helper to all the callsites. But
since you #ifdef out info->scrollmode we should catch them all I
guess.

> > Like I said in the cover letter I got mostly distracted with fbcon
> > locking last week, not really with this one here at all, so maybe
> > going with your 4 (or 2 if we squash them like I did here) patches is
> > neater?
>
> The benefit of my patch series was, that it could be easily backported first,
> and then cleaned up afterwards. Even a small additional backport patch to disable
> the fbcon acceleration for DRM in the old releases would be easy.
> But I'm not insisting on backporting the patches, if we find good way forward.
>
> So, either with the 4 (or 2) patches would be OK for me (or even your approach).

The idea behind the squash was that it's then impossible to backport
without the Kconfig, and so we'll only enable this code when people
intentionally want it. Maybe I'm too paranoid?

Anyway, you feel like finishing off your approach? Or should I send
out v2 of this with the issues fixed you spotted? Like I said either
is fine with me.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch