linux-kernel - Re: [PATCH 2/2] Revert "fbcon: Disable accelerated scrolling"

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Message-ID: <Ye7MnI7v7hK5GXQW@phenom.ffwll.local>
Date:   Mon, 24 Jan 2022 16:58:20 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Helge Deller <deller@....de>
Cc:     Javier Martinez Canillas <javierm@...hat.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Gerd Hoffmann <kraxel@...hat.com>, linux-fbdev@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sven Schnelle <svens@...ckframe.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Claudio Suarez <cssk@...-c.es>, Pavel Machek <pavel@....cz>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH 2/2] Revert "fbcon: Disable accelerated scrolling"

On Mon, Jan 24, 2022 at 04:29:34PM +0100, Helge Deller wrote:
> On 1/24/22 12:50, Javier Martinez Canillas wrote:
> > On 1/24/22 12:33, Thomas Zimmermann wrote:
> >
> > [snip]
> >
> >>> Thoughts?
> >>
> >> I can't say I approve keeping fbdev alive, but...
> >>
> >> With fbdev emulation, every DRM driver is an fbdev driver too. So
> >> CONFIG_FB_DRIVER is somewhat misleading. Better add an option like
> >> CONFIG_FBCON_HW_SCROLLING and have it selected by the fbdev drivers that
> >> absolutely need HW acceleration. That option would then protect the rsp
> >> code.
> 
> I'm not a fan of something like CONFIG_FBCON_HW_SCROLLING, but I'm not
> against it either.
> For me it sounds that this is not the real direction you want to go,
> which is to prevent that any other drivers take the framebuffer before
> you take it with simpledrm or similiar.
> CONFIG_FBCON_HW_SCROLLING IMHO just disables the (from your POV) neglectable accleration part.
> With an option like CONFIG_FB_DRIVER (maybe better: CONFIG_FB_LEGACY_DRIVERS)
> it's an easy option for distros to disable all of the legacy drivers
> from being built & shipped.
> 
> Instead of CONFIG_FBCON_HW_SCROLLING we could also choose
> CONFIG_FBCON_LEGACY_ACCELERATION, because it includes fillrect() as well...

+1 on that name, since on the lwn discussions I've also seen some noise
about resurrecting scrollback. And I guess we could do that too and then
just add it all behind that same option.
-Daniel

> > Agreed that this option would be better and allow distros
> > to disable the code that was reverted.
> 
> Yes, but IMHO it doesn't hurt either to leave it in.
> It doesn't break anything at least.
> Anyway...
> 
> Helge

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