drm/sysfb: Add efidrm for EFI displays

Add support for screen_info setups with VIDEO_TYPE_EFI. Provide the
minimum functionality of reading modes, updating and clearing the display.

There is existing support for these displays provided by simpledrm with
CONFIG_SYSFB_SIMPLEFB=y. Using efidrm over simpledrm will allows for the
mapping of video memory with correct caching. Simpledrm always assumes WC
caching, while fully cached memory is possible with efidrm. Efidrm will
also allow for the use of additional functionality provided by EFI, such
as EDID information.

In addition to efidrm, add struct pixel_format plus initializer macros.
The type and macros describe pixel formats in a generic way on order to
find the DRM format from the screen_info settings. Similar existing code
in SIMPLEFB_FORMATS and fbdev is not really what is needed in efidrm,
but SIMPLEFB_FORMATS can later be converted to struct pixel_format.

v4:
- depend on CONFIG_EFI
- disallow module for now as efi_mem_desc_lookup() is not exported
v3:
- depend on !SYSFB_SIMPLEFB (Javier)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20250401094056.32904-15-tzimmermann@suse.de

Author: tdz

drivers/gpu/drm/sysfb/Kconfig

@@ -7,6 +7,22 @@ config DRM_SYSFB_HELPER
 	tristate
 	depends on DRM
 
+config DRM_EFIDRM
+	bool "EFI framebuffer driver"
+	depends on (DRM=y) && MMU && EFI && (!SYSFB_SIMPLEFB || COMPILE_TEST)
+	select APERTURE_HELPERS
+	select DRM_CLIENT_SELECTION
+	select DRM_GEM_SHMEM_HELPER
+	select DRM_KMS_HELPER
+	select DRM_SYSFB_HELPER
+	select SYSFB
+	help
+	  DRM driver for EFI framebuffers.
+
+	  This driver assumes that the display hardware has been initialized
+	  by the firmware or bootloader before the kernel boots. Scanout
+	  buffer, size, and display format must be provided via EFI interfaces.
+
 config DRM_OFDRM
 	tristate "Open Firmware display driver"
 	depends on DRM && MMU && OF && (PPC || COMPILE_TEST)

drivers/gpu/drm/sysfb/Makefile

@@ -2,5 +2,6 @@
 
 obj-$(CONFIG_DRM_SYSFB_HELPER)	+= drm_sysfb_helper.o
 
+obj-$(CONFIG_DRM_EFIDRM)	+= efidrm.o
 obj-$(CONFIG_DRM_OFDRM)		+= ofdrm.o
 obj-$(CONFIG_DRM_SIMPLEDRM)	+= simpledrm.o