fbdev/core: Move logo functions into separate source file

Move the fbdev function for displaying boot-up logos into their
own file fb_logo.c. Only build fb_logo.c if CONFIG_LOGO has been
selected. No functional changes.

v2:
* include fb_internal.h (kernel test robot)
* simplify option-parsing ifdefs
* build fb_logo.o iff CONFIG_LOGO has been set

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230907085408.9354-6-tzimmermann@suse.de

fbdev/core: Unexport logo helpers

The interfaces for the fbdev logo are not used outside of the fbdev
module. Hence declare the fbdev logo functions in the internal header
file and remove their symbol exports. Only build the functions if
CONFIG_LOGO has been selected.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230907085408.9354-5-tzimmermann@suse.de

fbdev: Make support for userspace interfaces configurable

Add Kconfig option CONFIG_FB_DEVICE and make the virtual fbdev
device optional. If the new option has not been selected, fbdev
does not create files in devfs, sysfs or procfs.

Most modern Linux systems run a DRM-based graphics stack that uses
the kernel's framebuffer console, but has otherwise deprecated fbdev
support. Yet fbdev userspace interfaces are still present.

The option makes it possible to use the fbdev subsystem as console
implementation without support for userspace. This closes potential
entry points to manipulate kernel or I/O memory via framebuffers. It
also prevents the execution of driver code via ioctl or sysfs, both
of which might allow malicious software to exploit bugs in the fbdev
code.

A small number of fbdev drivers require struct fbinfo.dev to be
initialized, usually for the support of sysfs interface. Make these
drivers depend on FB_DEVICE. They can later be fixed if necessary.

v3:
* effect -> affect in Kconfig help (Daniel)
v2:
* set FB_DEVICE default to y (Geert)
* comment on {get,put}_device() (Sam)
* Kconfig fixes (Sam)
* add TODO item about FB_DEVICE dependencies (Sam)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-39-tzimmermann@suse.de

fbdev/core: Rework fb init code

Init the class "graphics" before the rest of fbdev. Later steps, such
as the sysfs code, depend on the class. Also arrange the module's exit
code in reverse order.

Unexport the global variable fb_class, which is only shared internally
within the fbdev core module.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-38-tzimmermann@suse.de

fbdev/core: Move file-I/O code into separate file

Move fbdev's file-I/O code into a separate file and contain it in
init and cleanup helpers. No functional changes.

v3:
* add missing file fb_chrdev.c
v2:
* rename source file (Sam)
* include <linux/compat.h> (Javier, kernel test robot)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-37-tzimmermann@suse.de

fbdev/core: Move procfs code to separate file

Move fbdev's procfs code into a separate file and contain it in
init and cleanup helpers. For the cleanup, replace remove_proc_entry()
with proc_remove(). It is equivalent in functionality, but looks
more like an inverse of proc_create_seq().

v2:
* document proc_remove() usage (Sam)
* revert unrelated removal of for_each_registered_fb()

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-36-tzimmermann@suse.de

fbdev/core: Add fb_device_{create,destroy}()

Move the logic to create and destroy fbdev devices into the new
helpers fb_device_create() and fb_device_destroy().

There was a call to fb_cleanup_device() in do_unregister_framebuffer()
that was too late. The device had already been removed at this point.
Move the call into fb_device_destroy().

Declare the helpers in the new internal header file fb_internal.h, as
they are only used within the fbdev core module.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-35-tzimmermann@suse.de