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

Atharva Tiwari
2026-02-06T12:57:11Z

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.

We use delayed work instead of a shutdown callback,
as it still applies the brightness
even during forced shutdowns and at 0% battery.

(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 | 91 +++++++++++++++++++
.../linux/platform_data/apple-brightness.h | 21 +++++
4 files changed, 123 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..c32e365dc511
--- /dev/null
+++ b/drivers/firmware/efi/apple-brightness.c
@@ -0,0 +1,91 @@
+// 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/cleanup.h>
+#include <linux/efi.h>
+#include <linux/mutex.h>
+#include <linux/workqueue.h>
+#include <linux/platform_data/apple-brightness.h>
+
+static DEFINE_MUTEX(apple_brightness_mutex);
+static struct delayed_work apple_brightness_work;
+
+static u32 efi_attr;
+static u16 last_saved_level;
+
+static int (*get_brightness)(struct backlight_device *bl);
+static struct backlight_device *bl_dev;
+
+static void apple_brightness_workfn(struct work_struct *work)
+{
+ u16 level;
+ efi_status_t status;
+
+ mutex_lock(&apple_brightness_mutex);
+
+ level = (u16)get_brightness(bl_dev);
+
+ if (level == last_saved_level)
+ goto out;
+
+ 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);
+ else
+ last_saved_level = level;
+
+out:
+ mutex_unlock(&apple_brightness_mutex);
+
+ mod_delayed_work(system_wq, &apple_brightness_work,
+ msecs_to_jiffies(APPLE_BRIGHTNESS_POLL));
+}
+
+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;
+
+ guard(mutex)(&apple_brightness_mutex);
+
+ 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;
+
+ bl_dev = bl;
+ get_brightness = get_brightnessfn;
+
+ INIT_DELAYED_WORK(&apple_brightness_work, apple_brightness_workfn);
+ mod_delayed_work(system_wq, &apple_brightness_work,
+ msecs_to_jiffies(APPLE_BRIGHTNESS_POLL));
+
+ 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..4cf5e2d346cb
--- /dev/null
+++ b/include/linux/platform_data/apple-brightness.h
@@ -0,0 +1,21 @@
+/* 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)
+
+#define APPLE_BRIGHTNESS_POLL 300
+
+int apple_brightness_probe(struct backlight_device *bl,
+ int (*get_brightnessfn)(struct backlight_device *bl));
+
+#endif /* _APPLE_BL_H */
--
2.43.0