[PATCH v2 1/2] efi: Save Brightness using EFI on Macs

[Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>]

Currently when a Mac reboots, the brightness is not the same
as the previous boot instead its the same as the last time the
Mac booted macOS.

We can fix this issue by saving the brightness level to the efivar
backlight-level.

(tested on iMac20,1)

Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>
---
 drivers/firmware/efi/Kconfig                  | 10 +++
 drivers/firmware/efi/Makefile                 |  1 +
 drivers/firmware/efi/apple-brightness.c       | 67 +++++++++++++++++++
 .../linux/platform_data/apple-brightness.h    | 20 ++++++
 4 files changed, 98 insertions(+)
 create mode 100644 drivers/firmware/efi/apple-brightness.c
 create mode 100644 include/linux/platform_data/apple-brightness.h

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 29e0729299f5..dd0a9c9a772a 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -167,6 +167,16 @@ config APPLE_PROPERTIES
 
 	  If unsure, say Y if you have a Mac.  Otherwise N.
 
+config APPLE_BRIGHTNESS
+	bool "Apple Backlight control for EFI"
+	depends on X86
+	help
+	  This will save the brightness level to EFI, so brightness
+	  level is preserved across reboots and shutdows. allowing
+	  for improved support of Apple hardware.
+
+	  If unsure, say Y if you have a Mac, Otherwise N.
+
 config RESET_ATTACK_MITIGATION
 	bool "Reset memory attack mitigation"
 	depends on EFI_STUB
diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
index 8efbcf699e4f..1f5705cc87a2 100644
--- a/drivers/firmware/efi/Makefile
+++ b/drivers/firmware/efi/Makefile
@@ -26,6 +26,7 @@ obj-$(CONFIG_EFI_BOOTLOADER_CONTROL)	+= efibc.o
 obj-$(CONFIG_EFI_TEST)			+= test/
 obj-$(CONFIG_EFI_DEV_PATH_PARSER)	+= dev-path-parser.o
 obj-$(CONFIG_APPLE_PROPERTIES)		+= apple-properties.o
+obj-$(CONFIG_APPLE_BRIGHTNESS)		+= apple-brightness.o
 obj-$(CONFIG_EFI_RCI2_TABLE)		+= rci2-table.o
 obj-$(CONFIG_EFI_EMBEDDED_FIRMWARE)	+= embedded-firmware.o
 obj-$(CONFIG_LOAD_UEFI_KEYS)		+= mokvar-table.o
diff --git a/drivers/firmware/efi/apple-brightness.c b/drivers/firmware/efi/apple-brightness.c
new file mode 100644
index 000000000000..b060861b0795
--- /dev/null
+++ b/drivers/firmware/efi/apple-brightness.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * apple-brightness.c - EFI brightness saver on Macs
+ * Copyright (C) 2026 Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/backlight.h>
+#include <linux/efi.h>
+#include <linux/platform_data/apple-brightness.h>
+
+static u32 efi_attr;
+static u16 last_saved_level;
+
+static int (*get_brightness)(struct backlight_device *bl);
+static struct backlight_device *bl_dev;
+
+void apple_brightness_shutdown(void)
+{
+	u16 level;
+	efi_status_t status;
+
+	level = (u16)get_brightness(bl_dev);
+
+	if (level == last_saved_level)
+		return;
+
+	status = efivar_set_variable(APPLE_BRIGHTNESS_NAME, &APPLE_BRIGHTNESS_GUID,
+				efi_attr, sizeof(level), &level);
+	if (status != EFI_SUCCESS)
+		pr_debug("Unable to set brightness: 0x%lx\n", status);
+}
+EXPORT_SYMBOL(apple_brightness_shutdown);
+
+int apple_brightness_probe(struct backlight_device *bl,
+	int (*get_brightnessfn)(struct backlight_device *bl))
+{
+	efi_status_t status;
+	unsigned long size = sizeof(last_saved_level);
+	int ret;
+
+	bl_dev = bl;
+	get_brightness = get_brightnessfn;
+
+	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_SET_VARIABLE))
+		return -ENODEV;
+
+	ret = efivar_lock();
+	if (ret)
+		return ret;
+
+	status = efivar_get_variable(APPLE_BRIGHTNESS_NAME, &APPLE_BRIGHTNESS_GUID,
+				&efi_attr, &size, &last_saved_level);
+
+	efivar_unlock();
+
+	if (status != EFI_SUCCESS)
+		return -ENODEV;
+
+	return 0;
+}
+EXPORT_SYMBOL(apple_brightness_probe);
+
+MODULE_AUTHOR("Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>");
+MODULE_DESCRIPTION("EFI Brightness saver for Macs");
+MODULE_LICENSE("Dual MIT/GPL");
diff --git a/include/linux/platform_data/apple-brightness.h b/include/linux/platform_data/apple-brightness.h
new file mode 100644
index 000000000000..54e3f3f8aa1c
--- /dev/null
+++ b/include/linux/platform_data/apple-brightness.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0-only OR MIT */
+/*
+ * apple-brightness.h - EFI brightness saver for Macs
+ * Copyright (C) 2026 Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>
+ */
+
+#ifndef _APPLE_BL_H_
+#define _APPLE_BL_H_
+
+#include <linux/backlight.h>
+#include <linux/efi.h>
+
+#define APPLE_BRIGHTNESS_NAME           L"backlight-level"
+#define APPLE_BRIGHTNESS_GUID           EFI_GUID(0x7c436110, 0xab2a, 0x4bbb, 0xa8, 0x80, 0xfe, 0x41, 0x99, 0x5c, 0x9f, 0x82)
+
+int apple_brightness_probe(struct backlight_device *bl,
+	int (*get_brightnessfn)(struct backlight_device *bl));
+
+void apple_brightness_shutdown(void);
+#endif /* _APPLE_BL_H */
-- 
2.43.0