drm/sysfb: corebootdrm: Add DRM driver for coreboot framebuffers

Add corebootdrm, a DRM driver for coreboot framebuffers. The driver
supports a pre-initialized framebuffer with various packed RGB formats.
The driver code is fairly small and uses the same logic as the other
sysfb drivers. Most of the implementation comes from existing sysfb
helpers.

Until now, coreboot relied on simpledrm or simplefb for boot-up graphics
output. Initialize the platform device for corebootdrm in the same place
in framebuffer_probe(). With a later commit, the simple-framebuffer should
be removed.

v4:
- sort include statements (Tzung-Bi)
v3:
- comment on _HAS_LFB semantics (Tzung-Bi)
- fix typo in commit description (Tzung-Bi)
- comment on simple-framebuffer being obsolete for coreboot
v2:
- reimplement as platform driver
- limit resources and mappings to known framebuffer memory; no
  page alignment
- create corebootdrm device from coreboot framebuffer code

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Julius Werner <jwerner@chromium.org>
Acked-by: Tzung-Bi Shih <tzungbi@kernel.org> # coreboot
Link: https://patch.msgid.link/20260217155836.96267-12-tzimmermann@suse.de

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/coreboot.h b/include/linux/coreboot.h
index 5746b99a070d..885da106fee3 100644
--- a/include/linux/coreboot.h
+++ b/include/linux/coreboot.h
@@ -13,6 +13,7 @@
 #define _LINUX_COREBOOT_H
 
 #include <linux/compiler_attributes.h>
+#include <linux/stddef.h>
 #include <linux/types.h>
 
 typedef __aligned(4) u64 cb_u64;
@@ -66,4 +67,11 @@ struct lb_framebuffer {
 	u8  reserved_mask_size;
 };
 
+/*
+ * True if the coreboot-provided data is large enough to hold information
+ * on the linear framebuffer. False otherwise.
+ */
+#define LB_FRAMEBUFFER_HAS_LFB(__fb) \
+	((__fb)->size >= offsetofend(struct lb_framebuffer, reserved_mask_size))
+
 #endif /* _LINUX_COREBOOT_H */