[PATCH v6 3/4] fbdev: Split frame buffer support in FB and FB_CORE symbols

From: Javier Martinez Canillas
Date: Wed Jul 19 2023 - 04:17:05 EST

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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@xxxxxxxxxx>
Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>
Tested-by: Arnd Bergmann <arnd@xxxxxxxx>
---

Changes in v6:
- Fix link error when CONFIG_FB_CORE=y and CONFIG_FB=m (Arnd Bergmann).

Changes in v5:
- Fix ifdef guard check in drivers/video/backlight/backlight.c (Arnd Bergmann).

Changes in v4:
- Fix menuconfig hierarchy that was broken in v3 (Arnd Bergmann).

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/backlight/backlight.c | 6 +++---
drivers/video/console/Kconfig | 2 +-
drivers/video/fbdev/Kconfig | 10 ++++++++--
drivers/video/fbdev/core/Kconfig | 30 ++++++++++++++++-------------
drivers/video/fbdev/core/Makefile | 10 ++++++----
7 files changed, 37 insertions(+), 25 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/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 9a885d398c22..86e1cdc8e369 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -79,8 +79,8 @@ static const char *const backlight_scale_types[] = {
[BACKLIGHT_SCALE_NON_LINEAR] = "non-linear",
};

-#if defined(CONFIG_FB) || (defined(CONFIG_FB_MODULE) && \
- defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
+#if defined(CONFIG_FB_CORE) || (defined(CONFIG_FB_CORE_MODULE) && \
+ defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
/*
* fb_notifier_callback
*
@@ -155,7 +155,7 @@ static inline int backlight_register_fb(struct backlight_device *bd)
static inline void backlight_unregister_fb(struct backlight_device *bd)
{
}
-#endif /* CONFIG_FB */
+#endif /* CONFIG_FB_CORE */

static void backlight_generate_event(struct backlight_device *bd,
enum backlight_update_reason reason)
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 ed881d5b3ee0..c0b0419e98b6 100644
--- a/drivers/video/fbdev/Kconfig
+++ b/drivers/video/fbdev/Kconfig
@@ -4,9 +4,9 @@
#

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
@@ -30,6 +30,12 @@ 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.

diff --git a/drivers/video/fbdev/core/Kconfig b/drivers/video/fbdev/core/Kconfig
index fd3b7f5b4b7a..528e4dd2199c 100644
--- a/drivers/video/fbdev/core/Kconfig
+++ b/drivers/video/fbdev/core/Kconfig
@@ -3,6 +3,10 @@
# fbdev core configuration
#

+config FB_CORE
+ select VIDEO_CMDLINE
+ tristate
+
config FB_NOTIFY
bool

@@ -23,7 +27,7 @@ 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
@@ -39,7 +43,7 @@ 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
@@ -47,7 +51,7 @@ 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)
@@ -55,7 +59,7 @@ 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
@@ -63,7 +67,7 @@ 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
@@ -71,7 +75,7 @@ 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
@@ -79,7 +83,7 @@ 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)
@@ -87,7 +91,7 @@ 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
@@ -126,22 +130,22 @@ 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
@@ -149,7 +153,7 @@ 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..edfde2948e5c 100644
--- a/drivers/video/fbdev/core/Makefile
+++ b/drivers/video/fbdev/core/Makefile
@@ -1,10 +1,12 @@
# 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-$(CONFIG_FB_CORE) += fb.o
+fb-y := fb_info.o \
+ fbmem.o fbcmap.o \
modedb.o fbcvt.o fb_cmdline.o fb_io_fops.o
+ifdef CONFIG_FB
+fb-y += fb_backlight.o fbmon.o
+endif
fb-$(CONFIG_FB_DEFERRED_IO) += fb_defio.o
fb-$(CONFIG_FB_DEVICE) += fb_chrdev.o \
fb_procfs.o \
--
2.41.0

Next message: Javier Martinez Canillas: "[PATCH v6 0/4] Allow disabling all native fbdev drivers and only keeping DRM emulation"
Previous message: Javier Martinez Canillas: "[PATCH v6 4/4] drm: Make FB_CORE to be selected if DRM fbdev emulation is enabled"
In reply to: Javier Martinez Canillas: "[PATCH v6 4/4] drm: Make FB_CORE to be selected if DRM fbdev emulation is enabled"
Next in thread: Javier Martinez Canillas: "[PATCH v6 1/4] video: Add auxiliary display drivers to Graphics support menu"
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