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([171.61.163.197]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35b9303eb9bsm3074980a91.8.2026.03.15.14.53.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Mar 2026 14:53:17 -0700 (PDT) From: Atharva Tiwari To: Cc: Atharva Tiwari , Lukas Wunner , Ard Biesheuvel , Hans de Goede , =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= , linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org Subject: [PATCH v2 1/2] efi: Save Brightness using EFI on Macs Date: Mon, 16 Mar 2026 03:22:41 +0530 Message-ID: <20260315215302.24087-2-atharvatiwarilinuxdev@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260315215302.24087-1-atharvatiwarilinuxdev@gmail.com> References: <20260315215302.24087-1-atharvatiwarilinuxdev@gmail.com> Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Atharva Tiwari --- 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 + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include +#include +#include + +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 "); +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 + */ + +#ifndef _APPLE_BL_H_ +#define _APPLE_BL_H_ + +#include +#include + +#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