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..243499a5d7b7 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 shutdowns. 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

> On 16 Mar 2026, at 9:03 PM, Atharva Tiwari <atharvatiwarilinuxdev@gmail.com> wrote:
> 
> 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

I tested this patch on a MacBookPro16,1, which is a T2 Intel Mac, and the behaviour is very weird:

1. macOS will never respect any brightness set by Linux
2. The Max brightness set by macOS is not the max brightness on Linux. I get these values on Linux:

aditya@MacBook:~$ efivar -p -n '7c436110-ab2a-4bbb-a880-fe41995c9f82-backlight-level'
GUID: 7c436110-ab2a-4bbb-a880-fe41995c9f82
Name: "backlight-level"
Attributes:
	Non-Volatile
	Boot Service Access
	Runtime Service Access
Value:
00000000  f1 02                                             |..              |

aditya@MacBook:~$ cat /sys/class/backlight/gmux_backlight/brightness
48238

3. I set the Max brightness on Linux, and restarted. I get this:

aditya@MacBook:~$ efivar -p -n '7c436110-ab2a-4bbb-a880-fe41995c9f82-backlight-level'
GUID: 7c436110-ab2a-4bbb-a880-fe41995c9f82
Name: "backlight-level"
Attributes:
	Non-Volatile
	Boot Service Access
	Runtime Service Access
Value:
00000000  7a ff                                             |z.              |

aditya@MacBook:~$ cat /sys/class/backlight/gmux_backlight/brightness
65402


4. Finally, any attempt to reduce the brightness seems worthless as unless booted back to macOS, Linux always boots at max brightness, but the nvram variable is changed successfully:

aditya@MacBook:~$ efivar -p -n '7c436110-ab2a-4bbb-a880-fe41995c9f82-backlight-level'
GUID: 7c436110-ab2a-4bbb-a880-fe41995c9f82
Name: "backlight-level"
Attributes:
	Non-Volatile
	Boot Service Access
	Runtime Service Access
Value:
00000000  eb 41                                             |.A              |

aditya@MacBook:~$ cat /sys/class/backlight/gmux_backlight/brightness
65402


Overall, it’s very inconsistent. Also, I’ve noticed Windows doesn't mess around with efivars, rather stores the brightness locally and implements it on every boot, something which systemd should do on Linux.