linux-kernel - Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

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Date:   Fri, 30 Jun 2023 13:19:04 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, Helge Deller <deller@....de>,
        Ingo Molnar <mingo@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only
 keeping DRM emulation

Hi Javier

Am 30.06.23 um 00:51 schrieb Javier Martinez Canillas:
> This patch series splits the fbdev core support in two different Kconfig
> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
> be disabled, while still having the the core fbdev support needed for the
> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
> disabling all fbdev drivers instead of having to be disabled individually.
> 
> The reason for doing this is that now with simpledrm, there's no need for
> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
> now disable them. But it would simplify the config a lot fo have a single
> Kconfig symbol to disable all fbdev drivers.

I still don't get the point of this change. We've disabled the fbdev 
drivers once. And they are off now and remain off.

The patchset now introduces FB_CORE, which just adds more options. But 
you're not reducing the code or compile time or any thing similar.

I'd like to suggest a change to these patches: rather then making FB and 
DRM_FBDEV_EMULATION depend on FB_CORE, make them select FB_CORE. That 
will allow the DRM subsystem to enable framebuffer emulation 
independently from framebuffer devices. If either has been set, the 
fbdev core will be selected.

Best regards
Thomas

> 
> I've build tested with possible combinations of CONFIG_FB, CONFIG_FB_CORE,
> CONFIG_DRM_FBDEV_EMULATION and CONFIG_FB_DEVICE symbols set to 'y' or 'n'.
> 
> Patch 1/2 makes the CONFIG_FB split that is mentioned above and patch 2/2
> makes DRM fbdev emulation depend on the new FB_CORE symbol instead of FB.
> 
> 
> Javier Martinez Canillas (2):
>    fbdev: Split frame buffer support in FB and FB_CORE symbols
>    drm: Make fbdev emulation depend on FB_CORE instead of FB
> 
>   arch/x86/Makefile                 |  2 +-
>   arch/x86/video/Makefile           |  2 +-
>   drivers/gpu/drm/Kconfig           |  2 +-
>   drivers/video/console/Kconfig     |  2 +-
>   drivers/video/fbdev/Kconfig       | 62 ++++++++++++++++++-------------
>   drivers/video/fbdev/core/Makefile | 14 +++----
>   6 files changed, 48 insertions(+), 36 deletions(-)
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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