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Date:   Mon, 24 Jan 2022 12:10:19 +0100
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Subject: Re: [PATCH 2/2] Revert "fbcon: Disable accelerated scrolling"
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To:     Gerd Hoffmann <kraxel@redhat.com>
Cc:     Thomas Zimmermann <tzimmermann@suse.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-fbdev@vger.kernel.org, Sven Schnelle <svens@stackframe.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Javier Martinez Canillas <javierm@redhat.com>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Ilia Mirkin <imirkin@alum.mit.edu>,
        Tomi Valkeinen <tomi.valkeinen@ti.com>,
        dri-devel@lists.freedesktop.org,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Sam Ravnborg <sam@ravnborg.org>, Claudio Suarez <cssk@net-c.es>
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 <20220119110839.33187-3-deller@gmx.de> <YelyGDNDTn1Aq/hm@phenom.ffwll.local>
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 <20220121072006.ylw2hdl7jbkbwnre@sirius.home.kraxel.org>
From:   Helge Deller <deller@gmx.de>
In-Reply-To: <20220121072006.ylw2hdl7jbkbwnre@sirius.home.kraxel.org>
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On 1/21/22 08:20, Gerd Hoffmann wrote:
>>> So if this really has to come back then I think the pragmatic approach=
 is
>>> to do it behind a CONFIG_FBCON_ACCEL, default n, and with a huge warni=
ng
>>> that enabling that shouldn't be done for any distro which only enables
>>> firmware and drm fbdev drivers.
>>
>> Thanks for coming back on this, but quite frankly I don't understand
>> that request. How should that warning look like, something along:
>> "BE WARNED: The framebuffer text console on your non-DRM supported
>> graphic card will then run faster and smoother if you enable this optio=
n."
>> That doesn't make sense. People and distros would want to enable that.
>
> Nope.  Most distros want disable fbdev drivers rather sooner than later.
> The fbdev drivers enabled in the fedora kernel today:
>
> 	CONFIG_FB_VGA16=3Dm
> 	CONFIG_FB_VESA=3Dy
> 	CONFIG_FB_EFI=3Dy
> 	CONFIG_FB_SSD1307=3Dm
>
> CONFIG_FB_VESA + CONFIG_FB_EFI will go away soon, with simpledrm taking
> over their role.

That's Ok.
Nevertheless, some distros and platforms will still need fbdev drivers for
various reasons.


>> And if a distro *just* has firmware and drm fbdev drivers enabled,
>> none of the non-DRM graphic cards would be loaded anyway and this code
>> wouldn't be executed anyway.
>
> Yes, exactly.  That's why there is no point in compiling that code.

As long as you have a graphic card which is not supported by DRM you still=
 need it.

Here is my proposed way forward:
a) I will resend the patches which reverts the remove-fbcon-hardware-scoll=
ing 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 me=
rge 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 exclud=
e 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 Kconf=
ig files.
c) That way we can use "#if defined(CONFIG_FB_DRIVERS).." to exclude code =
in fbcon which
   isn't needed by DRM.

Thoughts?

Helge