[PATCH v3 2/3] fbdev: Split frame buffer support in FB and FB_CORE symbols

[Javier Martinez Canillas <javierm@redhat.com>]

Currently the CONFIG_FB option has to be enabled even if no legacy fbdev
drivers are needed (e.g: only to have support for framebuffer consoles).

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 and/or the DRM fbdev emulation layer.

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

Nothing from fb_backlight.o and fbmon.o is used by the DRM fbdev emulation
layer so these two objects can be compiled out when CONFIG_FB is disabled.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

Changes in v3:
- Really make a hidden symbol by removing the prompt (Arnd Bergmann).
- Change FB_CORE to config instead of menuconfig (Arnd Bergmann).
- Keep "depends on FB" for FIRMWARE_EDID (Arnd Bergmann).
- Compile out fb_backlight.o and fbmon.o that are only needed for FB
  (Arnd Bergmann).
- Make FB_DEVICE to depend on FB_CORE instead of selecting it.

Changes in v2:
- Keep "depends on FB" for FB_DDC, FB_HECUBA, FB_SVGALIB, FB_MACMODES,
  FB_BACKLIGHT, FB_MODE_HELPERS and FB_TILEBLITTING (Arnd Bergmann).
- Don't change the fb.o object name (Arnd Bergmann).
- Make FB_CORE a non-visible Kconfig symbol instead (Thomas Zimmermann).

 arch/x86/Makefile                 |  2 +-
 arch/x86/video/Makefile           |  2 +-
 drivers/video/console/Kconfig     |  2 +-
 drivers/video/fbdev/Kconfig       | 40 +++++++++++++++++++------------
 drivers/video/fbdev/core/Makefile |  8 +++----
 5 files changed, 32 insertions(+), 22 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index b39975977c03..89a02e69be5f 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -259,7 +259,7 @@ 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 11640c116115..5ebe48752ffc 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 a2a88d42edf0..1b5a319971ed 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -72,7 +72,7 @@ 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 cecf15418632..d436a4fd6f0a 100644
--- a/drivers/video/fbdev/Kconfig
+++ b/drivers/video/fbdev/Kconfig
@@ -6,10 +6,14 @@
 config FB_NOTIFY
 	bool
 
+config FB_CORE
+	select VIDEO_CMDLINE
+	tristate
+
 menuconfig FB
-	tristate "Support for frame buffer devices"
+	tristate "Support for frame buffer device drivers"
+	select FB_CORE
 	select FB_NOTIFY
-	select VIDEO_CMDLINE
 	help
 	  The frame buffer device provides an abstraction for the graphics
 	  hardware. It represents the frame buffer of some video hardware and
@@ -33,6 +37,12 @@ menuconfig FB
 	  <http://www.munted.org.uk/programming/Framebuffer-HOWTO-1.3.html> for more
 	  information.
 
+	  This enables support for native frame buffer device (fbdev) drivers.
+
+	  The DRM subsystem provides support for emulated frame buffer devices
+	  on top of KMS drivers, 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.
 
@@ -59,7 +69,7 @@ config FIRMWARE_EDID
 
 config FB_DEVICE
 	bool "Provide legacy /dev/fb* device"
-	depends on FB
+	depends on FB_CORE
 	default y
 	help
 	  Say Y here if you want the legacy /dev/fb* device file and
@@ -75,7 +85,7 @@ config FB_DDC
 
 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 +93,7 @@ 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 +101,7 @@ 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 +109,7 @@ 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 +117,7 @@ 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 +125,7 @@ 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 +133,7 @@ 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
@@ -162,22 +172,22 @@ 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_IO_HELPERS
 	bool
-	depends on FB
+	depends on FB_CORE
 	select FB_CFB_COPYAREA
 	select FB_CFB_FILLRECT
 	select FB_CFB_IMAGEBLIT
 
 config FB_SYS_HELPERS
 	bool
-	depends on FB
+	depends on FB_CORE
 	select FB_SYS_COPYAREA
 	select FB_SYS_FILLRECT
 	select FB_SYS_FOPS
@@ -185,7 +195,7 @@ config FB_SYS_HELPERS
 
 config FB_SYS_HELPERS_DEFERRED
 	bool
-	depends on FB
+	depends on FB_CORE
 	select FB_DEFERRED_IO
 	select FB_SYS_HELPERS
 
diff --git a/drivers/video/fbdev/core/Makefile b/drivers/video/fbdev/core/Makefile
index 9150bafd9e89..2cd213716c12 100644
--- a/drivers/video/fbdev/core/Makefile
+++ b/drivers/video/fbdev/core/Makefile
@@ -1,10 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_FB_NOTIFY)           += fb_notify.o
-obj-$(CONFIG_FB)                  += fb.o
-fb-y                              := fb_backlight.o \
-                                     fb_info.o \
-                                     fbmem.o fbmon.o fbcmap.o \
+obj-$(CONFIG_FB_CORE)             += fb.o
+fb-y                              := fb_info.o \
+                                     fbmem.o fbcmap.o \
                                      modedb.o fbcvt.o fb_cmdline.o fb_io_fops.o
+fb-$(CONFIG_FB)                   += fb_backlight.o fbmon.o
 fb-$(CONFIG_FB_DEFERRED_IO)       += fb_defio.o
 fb-$(CONFIG_FB_DEVICE)            += fb_chrdev.o \
                                      fb_procfs.o \
-- 
2.41.0