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

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Message-ID: <d23800b4-503c-a6e2-2c51-2c07a736dffc@suse.de>
Date:   Mon, 24 Jan 2022 12:33:21 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Helge Deller <deller@....de>, Gerd Hoffmann <kraxel@...hat.com>
Cc:     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>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Claudio Suarez <cssk@...-c.es>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 2/2] Revert "fbcon: Disable accelerated scrolling"

Hi

Am 24.01.22 um 12:10 schrieb Helge Deller:
[...]
> 
> Here is my proposed way forward:
> a) I will resend the patches which reverts the remove-fbcon-hardware-scolling patches
>     to the mailing lists. I'll adjust the stable tags and update the commit messages.
> b) Then after some days I'll include it in the fbdev for-next git branch. That way it's
>     included in the various build & test chains.
> c) If everything is working well, I'll push that change during the next merge window
>     for kernel 5.18. If problems arise we will need to discuss.
> 
> While the patches are in the fbdev git tree we should decide how to exclude code
> which is not needed for DRM.
> 
> What about this proposal:
> a) adding a Kconfig option like:
>     CONFIG_FB_DRIVERS - enable if you need the fbdev drivers. For DRM-only this should be disabled.
> b) Add to every native fbdev driver a "depends on FB_DRIVERS" in the Kconfig files.
> c) That way we can use "#if defined(CONFIG_FB_DRIVERS).." to exclude code in fbcon which
>     isn't needed by DRM.
> 
> 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.

Best regards
Thomas

> 
> Helge

-- 
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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