[RFC PATCH 3/4] fbdev: Split frame buffer support in FB and FB_CORE symbols

From: Javier Martinez Canillas
Date: Fri Aug 27 2021 - 06:05:47 EST

Currently the CONFIG_FB option has to be enabled even if no legacy fbdev
drivers are needed, in order to have support for a framebuffer console.

The DRM subsystem has a fbdev emulation layer, but depends on CONFIG_FB
and so it can only be enabled if that dependency is enabled as well.

That means fbdev drivers have to be explicitly disabled if users want to
enable CONFIG_FB, only to use fbcon with the DRM fbdev emulation layer.

This patch introduces a CONFIG_FB_CORE option that could be enabled just
to have the core support needed for CONFIG_DRM_FBDEV_EMULATION, allowing
CONFIG_FB to be disabled (and automatically disabling all fbdev drivers).

The fbsysfs.o object is left out of fb_core.o, because that's not needed
for KMS drivers and the DRM fbdev emulation layer.

Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
---

arch/x86/Makefile | 2 +-
arch/x86/video/Makefile | 2 +-
drivers/video/console/Kconfig | 2 +-
drivers/video/fbdev/Kconfig | 57 ++++++++++++++++++-------------
drivers/video/fbdev/core/Makefile | 13 ++++---
include/linux/fb.h | 14 ++++++++
6 files changed, 59 insertions(+), 31 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 44dd071d836..dc409539218 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -229,7 +229,7 @@ drivers-$(CONFIG_PCI) += arch/x86/pci/
# suspend and hibernation support
drivers-$(CONFIG_PM) += arch/x86/power/

-drivers-$(CONFIG_FB) += arch/x86/video/
+drivers-$(CONFIG_FB_CORE) += arch/x86/video/

####
# boot loader support. Several targets are kept for legacy purposes
diff --git a/arch/x86/video/Makefile b/arch/x86/video/Makefile
index 11640c11611..cb0735bd662 100644
--- a/arch/x86/video/Makefile
+++ b/arch/x86/video/Makefile
@@ -1,2 +1,2 @@
# SPDX-License-Identifier: GPL-2.0-only
-obj-$(CONFIG_FB) += fbdev.o
+obj-$(CONFIG_FB_CORE) += fbdev.o
diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 840d9813b0b..0c562ed3495 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -71,7 +71,7 @@ config DUMMY_CONSOLE_ROWS

config FRAMEBUFFER_CONSOLE
bool "Framebuffer Console support"
- depends on FB && !UML
+ depends on FB_CORE && !UML
select VT_HW_CONSOLE_BINDING
select CRC32
select FONT_SUPPORT
diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
index d33c5cd684c..cb9e8b503a5 100644
--- a/drivers/video/fbdev/Kconfig
+++ b/drivers/video/fbdev/Kconfig
@@ -9,10 +9,8 @@ config FB_CMDLINE
config FB_NOTIFY
bool

-menuconfig FB
- tristate "Support for frame buffer devices"
- select FB_CMDLINE
- select FB_NOTIFY
+menuconfig FB_CORE
+ tristate "Core support for frame buffer devices"
help
The frame buffer device provides an abstraction for the graphics
hardware. It represents the frame buffer of some video hardware and
@@ -36,6 +34,19 @@ menuconfig FB
<http://www.munted.org.uk/programming/Framebuffer-HOWTO-1.3.html> for more
information.

+ This options enables the core support for frame buffer devices.
+
+menuconfig FB
+ tristate "Support for frame buffer device drivers"
+ depends on FB_CORE
+ select FB_CMDLINE
+ select FB_NOTIFY
+ help
+ This enables support for frame buffer devices (fbdev) drivers.
+
+ The DRM subsystem provides an option to emulate fbdev devices but
+ this option allows legacy fbdev drivers to be enabled as well.
+
Say Y here and to the driver for your graphics board below if you
are compiling a kernel for a non-x86 architecture.

@@ -47,7 +58,7 @@ menuconfig FB

config FIRMWARE_EDID
bool "Enable firmware EDID"
- depends on FB
+ depends on FB_CORE
help
This enables access to the EDID transferred from the firmware.
On the i386, this is from the Video BIOS. Enable this if DDC/I2C
@@ -62,7 +73,7 @@ config FIRMWARE_EDID

config FB_DDC
tristate
- depends on FB
+ depends on FB_CORE
select I2C_ALGOBIT
select I2C

@@ -75,7 +86,7 @@ config FB_BOOT_VESA_SUPPORT

config FB_CFB_FILLRECT
tristate
- depends on FB
+ depends on FB_CORE
help
Include the cfb_fillrect function for generic software rectangle
filling. This is used by drivers that don't provide their own
@@ -83,7 +94,7 @@ config FB_CFB_FILLRECT

config FB_CFB_COPYAREA
tristate
- depends on FB
+ depends on FB_CORE
help
Include the cfb_copyarea function for generic software area copying.
This is used by drivers that don't provide their own (accelerated)
@@ -91,7 +102,7 @@ config FB_CFB_COPYAREA

config FB_CFB_IMAGEBLIT
tristate
- depends on FB
+ depends on FB_CORE
help
Include the cfb_imageblit function for generic software image
blitting. This is used by drivers that don't provide their own
@@ -99,7 +110,7 @@ config FB_CFB_IMAGEBLIT

config FB_CFB_REV_PIXELS_IN_BYTE
bool
- depends on FB
+ depends on FB_CORE
help
Allow generic frame-buffer functions to work on displays with 1, 2
and 4 bits per pixel depths which has opposite order of pixels in
@@ -107,7 +118,7 @@ config FB_CFB_REV_PIXELS_IN_BYTE

config FB_SYS_FILLRECT
tristate
- depends on FB
+ depends on FB_CORE
help
Include the sys_fillrect function for generic software rectangle
filling. This is used by drivers that don't provide their own
@@ -115,7 +126,7 @@ config FB_SYS_FILLRECT

config FB_SYS_COPYAREA
tristate
- depends on FB
+ depends on FB_CORE
help
Include the sys_copyarea function for generic software area copying.
This is used by drivers that don't provide their own (accelerated)
@@ -123,7 +134,7 @@ config FB_SYS_COPYAREA

config FB_SYS_IMAGEBLIT
tristate
- depends on FB
+ depends on FB_CORE
help
Include the sys_imageblit function for generic software image
blitting. This is used by drivers that don't provide their own
@@ -131,14 +142,14 @@ config FB_SYS_IMAGEBLIT

config FB_PROVIDE_GET_FB_UNMAPPED_AREA
bool
- depends on FB
+ depends on FB_CORE
help
Allow generic frame-buffer to provide get_fb_unmapped_area
function.

menuconfig FB_FOREIGN_ENDIAN
bool "Framebuffer foreign endianness support"
- depends on FB
+ depends on FB_CORE
help
This menu will let you enable support for the framebuffers with
non-native endianness (e.g. Little-Endian framebuffer on a
@@ -162,36 +173,36 @@ endchoice

config FB_SYS_FOPS
tristate
- depends on FB
+ depends on FB_CORE

config FB_DEFERRED_IO
bool
- depends on FB
+ depends on FB_CORE

config FB_HECUBA
tristate
- depends on FB
+ depends on FB_CORE
depends on FB_DEFERRED_IO

config FB_SVGALIB
tristate
- depends on FB
+ depends on FB_CORE
help
Common utility functions useful to fbdev drivers of VGA-based
cards.

config FB_MACMODES
tristate
- depends on FB
+ depends on FB_CORE

config FB_BACKLIGHT
tristate
- depends on FB
+ depends on FB_CORE
select BACKLIGHT_CLASS_DEVICE

config FB_MODE_HELPERS
bool "Enable Video Mode Handling Helpers"
- depends on FB
+ depends on FB_CORE
help
This enables functions for handling video modes using the
Generalized Timing Formula and the EDID parser. A few drivers rely
@@ -201,7 +212,7 @@ config FB_MODE_HELPERS

config FB_TILEBLITTING
bool "Enable Tile Blitting Support"
- depends on FB
+ depends on FB_CORE
help
This enables tile blitting. Tile blitting is a drawing technique
where the screen is divided into rectangular sections (tiles), whereas
diff --git a/drivers/video/fbdev/core/Makefile b/drivers/video/fbdev/core/Makefile
index 26cbc965497..328a017c78b 100644
--- a/drivers/video/fbdev/core/Makefile
+++ b/drivers/video/fbdev/core/Makefile
@@ -1,22 +1,25 @@
# SPDX-License-Identifier: GPL-2.0
obj-$(CONFIG_FB_CMDLINE) += fb_cmdline.o
obj-$(CONFIG_FB_NOTIFY) += fb_notify.o
+obj-$(CONFIG_FB_CORE) += fb_core.o
obj-$(CONFIG_FB) += fb.o
-fb-y := fbmem.o fbmon.o fbcmap.o fbsysfs.o \
+fb_core-y := fbmem.o fbmon.o fbcmap.o \
modedb.o fbcvt.o
-fb-$(CONFIG_FB_DEFERRED_IO) += fb_defio.o
+fb_core-$(CONFIG_FB_DEFERRED_IO) += fb_defio.o

ifeq ($(CONFIG_FRAMEBUFFER_CONSOLE),y)
-fb-y += fbcon.o bitblit.o softcursor.o
+fb_core-y += fbcon.o bitblit.o softcursor.o
ifeq ($(CONFIG_FB_TILEBLITTING),y)
-fb-y += tileblit.o
+fb_core-y += tileblit.o
endif
ifeq ($(CONFIG_FRAMEBUFFER_CONSOLE_ROTATION),y)
-fb-y += fbcon_rotate.o fbcon_cw.o fbcon_ud.o \
+fb_core-y += fbcon_rotate.o fbcon_cw.o fbcon_ud.o \
fbcon_ccw.o
endif
endif

+fb-y := fbsysfs.o
+
obj-$(CONFIG_FB_CFB_FILLRECT) += cfbfillrect.o
obj-$(CONFIG_FB_CFB_COPYAREA) += cfbcopyarea.o
obj-$(CONFIG_FB_CFB_IMAGEBLIT) += cfbimgblt.o
diff --git a/include/linux/fb.h b/include/linux/fb.h
index 96111248a25..f66eefbf1ee 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -689,9 +689,23 @@ static inline bool fb_be_math(struct fb_info *info)
/* drivers/video/fbsysfs.c */
extern struct fb_info *framebuffer_alloc(size_t size, struct device *dev);
extern void framebuffer_release(struct fb_info *info);
+#if IS_ENABLED(CONFIG_FB)
extern int fb_register_sysfs(struct fb_info *fb_info);
extern void fb_unregister_sysfs(struct fb_info *head);
extern void fb_bl_default_curve(struct fb_info *fb_info, u8 off, u8 min, u8 max);
+#else
+static inline int fb_register_sysfs(struct fb_info *fb_info)
+{
+ return 0;
+}
+static inline void fb_unregister_sysfs(struct fb_info *head)
+{
+}
+static inline void fb_bl_default_curve(struct fb_info *fb_info, u8 off,
+ u8 min, u8 max)
+{
+}
+#endif

/* drivers/video/fbmon.c */
#define FB_MAXTIMINGS 0
--
2.31.1