[PATCH v2 08/10] efi: Support EDID information

Thomas Zimmermann
2025-11-24T16:52:09Z

Add LINUX_EFI_PRIMARY_DISPLAY_TABLE_GUID to the list of config-table
UUIDs. Read sysfb_primary_display from the entry. The UUID has been
generated with uuidgen.

Still support LINUX_EFI_SCREEN_INFO_TABLE_GUID as fallback in case an
older boot loader invokes the kernel.

If CONFIG_FIRMWARE_EDID=n, EDID information is disabled.

Make the Kconfig symbol CONFIG_FIRMWARE_EDID available with EFI. Setting
the value to 'n' disables EDID support.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
arch/loongarch/kernel/efi.c | 14 +++++++++++++-
drivers/firmware/efi/efi-init.c | 14 +++++++++++++-
drivers/firmware/efi/efi.c | 2 ++
drivers/video/Kconfig | 8 +++++---
include/linux/efi.h | 8 +++++---
5 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/arch/loongarch/kernel/efi.c b/arch/loongarch/kernel/efi.c
index 1ef38036e8ae..2d90758e5037 100644
--- a/arch/loongarch/kernel/efi.c
+++ b/arch/loongarch/kernel/efi.c
@@ -72,6 +72,7 @@ bool efi_poweroff_required(void)
(acpi_gbl_reduced_hardware || acpi_no_s5);
}

+unsigned long __initdata primary_display_table = EFI_INVALID_TABLE_ADDR;
unsigned long __initdata screen_info_table = EFI_INVALID_TABLE_ADDR;

#if defined(CONFIG_SYSFB) || defined(CONFIG_EFI_EARLYCON)
@@ -81,7 +82,18 @@ EXPORT_SYMBOL_GPL(sysfb_primary_display);

static void __init init_primary_display(void)
{
- if (screen_info_table == EFI_INVALID_TABLE_ADDR) {
+ if (primary_display_table != EFI_INVALID_TABLE_ADDR) {
+ struct sysfb_display_info *dpy =
+ early_memremap(primary_display_table, sizeof(*dpy));
+
+ if (!dpy) {
+ pr_err("Could not map primary_display config table\n");
+ return;
+ }
+ sysfb_primary_display = *dpy;
+ memset(dpy, 0, sizeof(*dpy));
+ early_memunmap(dpy, sizeof(*dpy));
+ } else if (screen_info_table != EFI_INVALID_TABLE_ADDR) {
struct screen_info *si = early_memremap(screen_info_table, sizeof(*si));

if (!si) {
diff --git a/drivers/firmware/efi/efi-init.c b/drivers/firmware/efi/efi-init.c
index ca697d485116..0f167c0e058e 100644
--- a/drivers/firmware/efi/efi-init.c
+++ b/drivers/firmware/efi/efi-init.c
@@ -23,6 +23,7 @@

#include <asm/efi.h>

+unsigned long __initdata primary_display_table = EFI_INVALID_TABLE_ADDR;
unsigned long __initdata screen_info_table = EFI_INVALID_TABLE_ADDR;

static int __init is_memory(efi_memory_desc_t *md)
@@ -67,7 +68,18 @@ EXPORT_SYMBOL_GPL(sysfb_primary_display);

static void __init init_primary_display(void)
{
- if (screen_info_table != EFI_INVALID_TABLE_ADDR) {
+ if (primary_display_table != EFI_INVALID_TABLE_ADDR) {
+ struct sysfb_display_info *dpy =
+ early_memremap(primary_display_table, sizeof(*dpy));
+
+ if (!dpy) {
+ pr_err("Could not map primary_display config table\n");
+ return;
+ }
+ sysfb_primary_display = *dpy;
+ memset(dpy, 0, sizeof(*dpy));
+ early_memunmap(dpy, sizeof(*dpy));
+ } else if (screen_info_table != EFI_INVALID_TABLE_ADDR) {
struct screen_info *si = early_memremap(screen_info_table, sizeof(*si));

if (!si) {
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index a9070d00b833..c07f0878a4d6 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -63,6 +63,7 @@ static unsigned long __initdata mem_reserve = EFI_INVALID_TABLE_ADDR;
static unsigned long __initdata rt_prop = EFI_INVALID_TABLE_ADDR;
static unsigned long __initdata initrd = EFI_INVALID_TABLE_ADDR;

+extern unsigned long primary_display_table;
extern unsigned long screen_info_table;

struct mm_struct efi_mm = {
@@ -641,6 +642,7 @@ static const efi_config_table_type_t common_tables[] __initconst = {
{LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID, &efi.unaccepted, "Unaccepted" },
#endif
#ifdef CONFIG_EFI_GENERIC_STUB
+ {LINUX_EFI_PRIMARY_DISPLAY_TABLE_GUID, &primary_display_table },
{LINUX_EFI_SCREEN_INFO_TABLE_GUID, &screen_info_table },
#endif
{},
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index d51777df12d1..f452fac90a9f 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -63,11 +63,13 @@ endif # HAS_IOMEM

config FIRMWARE_EDID
bool "Enable firmware EDID"
- depends on X86
+ depends on EFI || X86
help
This enables access to the EDID transferred from the firmware.
- On x86, this is from the VESA BIOS. DRM display drivers will
- be able to export the information to userspace.
+ On EFI systems, the EDID comes from the same device as the
+ primary GOP. On x86 with BIOS, it comes from the VESA BIOS.
+ DRM display drivers will be able to export the information
+ to userspace.

Also enable this if DDC/I2C transfers do not work for your driver
and if you are using nvidiafb, i810fb or savagefb.
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 2a43094e23f7..f645bcc66ee2 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -406,11 +406,13 @@ void efi_native_runtime_setup(void);
#define EFI_CC_FINAL_EVENTS_TABLE_GUID EFI_GUID(0xdd4a4648, 0x2de7, 0x4665, 0x96, 0x4d, 0x21, 0xd9, 0xef, 0x5f, 0xb4, 0x46)

/*
- * This GUID is used to pass to the kernel proper the struct screen_info
- * structure that was populated by the stub based on the GOP protocol instance
- * associated with ConOut
+ * These GUIDs are used to pass to the kernel proper the info
+ * structures that were populated by the stub based on the GOP
+ * instance associated with ConOut.
*/
+#define LINUX_EFI_PRIMARY_DISPLAY_TABLE_GUID EFI_GUID(0x8700a405, 0xcda4, 0x46d4, 0xb8, 0xc3, 0x04, 0xe5, 0xcd, 0xb4, 0x30, 0x21)
#define LINUX_EFI_SCREEN_INFO_TABLE_GUID EFI_GUID(0xe03fc20a, 0x85dc, 0x406e, 0xb9, 0x0e, 0x4a, 0xb5, 0x02, 0x37, 0x1d, 0x95)
+
#define LINUX_EFI_ARM_CPU_STATE_TABLE_GUID EFI_GUID(0xef79e4aa, 0x3c3d, 0x4989, 0xb9, 0x02, 0x07, 0xa9, 0x43, 0xe5, 0x50, 0xd2)
#define LINUX_EFI_LOADER_ENTRY_GUID EFI_GUID(0x4a67b082, 0x0a4c, 0x41cf, 0xb6, 0xc7, 0x44, 0x0b, 0x29, 0xbb, 0x8c, 0x4f)
#define LINUX_EFI_RANDOM_SEED_TABLE_GUID EFI_GUID(0x1ce1e5bc, 0x7ceb, 0x42f2, 0x81, 0xe5, 0x8a, 0xad, 0xf1, 0x80, 0xf5, 0x7b)
--
2.51.1