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

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Date:   Mon, 24 Jan 2022 16:45:06 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Helge Deller <deller@....de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>
Cc:     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"

Hi

Am 24.01.22 um 16:29 schrieb Helge Deller:
> 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.

These drivers have been disabled by most distros a long time ago. Those 
that still remain are the generic, soon to be replaced, ones; and 
drivers for niche architectures where no DRM-based replacement exists.

If I run DRM with fbdev emulation, HW scrolling is unused, possibly 
buggy, and I'd want to not built it if possible. I guess that's what 
most distros would want as well. That's the use case for FBCON_HW_SCROLLING.

Best regards
Thomas


-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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