linux-kernel - [RFC PATCH 0/4] Allow to use DRM fbdev emulation layer with CONFIG

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Date:   Fri, 27 Aug 2021 12:00:23 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     "H . Peter Anvin" <hpa@...or.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        x86@...nel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-fbdev@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Maxime Ripard <mripard@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Peter Robinson <pbrobinson@...il.com>,
        Hans de Goede <hdegoede@...hat.com>,
        dri-devel@...ts.freedesktop.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel@...ll.ch>,
        Ingo Molnar <mingo@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Javier Martinez Canillas <javierm@...hat.com>
Subject: [RFC PATCH 0/4] Allow to use DRM fbdev emulation layer with CONFIG_FB disabled

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 using fbcon with the DRM fbdev emulation layer.

The reason for doing this is that now with simpledrm we could just boot
with simpledrm -> real DRM driver, without needing any legacy fbdev driver
(e.g: efifb or simplefb) even for the early console.

We want to do that in the Fedora kernel, but currently need to keep option
CONFIG_FB enabled and all fbdev drivers explicitly disabled, which makes
the configuration harder to maintain.

It is a RFC because I'm not that familiar with the fbdev core, but I have
tested and works with CONFIG_DRM_FBDEV_EMULATION=y and CONFIG_FB disabled.
This config automatically disables all the fbdev drivers that is our goal.

Patch 1/4 is just a clean up, patch 2/4 moves a couple of functions out of
fbsysfs.o, that are not related to sysfs attributes creation and finally
patch 3/4 makes the fbdev split that is mentioned above.

Patch 4/4 makes the DRM fbdev emulation depend on the new FB_CORE symbol
instead of FB. This could be done as a follow-up but for completeness is
also included in this series.

Best regards,
Javier

Javier Martinez Canillas (4):
  fbdev: Rename fb_*_device() functions names to match what they do
  fbdev: Move framebuffer_{alloc,release}() functions to fbmem.c
  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        | 57 +++++++++++++---------
 drivers/video/fbdev/core/Makefile  | 13 +++--
 drivers/video/fbdev/core/fbmem.c   | 73 ++++++++++++++++++++++++++--
 drivers/video/fbdev/core/fbsysfs.c | 77 +-----------------------------
 include/linux/fb.h                 | 18 ++++++-
 9 files changed, 134 insertions(+), 112 deletions(-)

-- 
2.31.1