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* [RFC PATCH 3/4] fbdev: Split frame buffer support in FB and FB_CORE symbols
@ 2021-08-27 10:05 Javier Martinez Canillas
  0 siblings, 0 replies; only message in thread
From: Javier Martinez Canillas @ 2021-08-27 10:05 UTC (permalink / raw)
  To: linux-kernel
  Cc: H . Peter Anvin, Peter Robinson, Thomas Zimmermann,
	Maxime Ripard, Hans de Goede, Daniel Vetter, x86, dri-devel,
	linux-fbdev, David Airlie, Maarten Lankhorst, Borislav Petkov,
	Ingo Molnar, Thomas Gleixner, Greg Kroah-Hartman,
	Javier Martinez Canillas

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@redhat.com>
---

 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


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