Hi All, I recently learned that some Dell AIOs (1) use a backlight controller board connected to an UART. Canonical even submitted a driver for this in 2017: https://lkml.org/lkml/2017/10/26/78 This UART has a DELL0501 HID with CID set to PNP0501 so that the UART is still handled by 8250_pnp.c. Unfortunately there is no separate ACPI device with an UartSerialBusV2() resource to model the backlight-controller. An ACPI quirk has been merged recently to deal with this and create a serdev controller for the UART despite the missing UartSerialBusV2() resource: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=99b572e6136eab69a8c91d72cf8595b256e304b5 Patch 1 in this series adds a driver binding to the "dell-uart-backlight" device created by this quirk. This drivers creates a serdev-device for the DELL0501 serdev-controller and registers a serdev backlight driver which binds to this serdev-device. Patch 2 contains a small emulator for the UART attached backlight controller found on this Dell AOIs, I wrote and used this to develop the driver since I did not have access to such an AOI myself. This has been successfully tested by Roman Bogoyev (who originally reported the missing driver to me by email) on a Dell Inspiron 27 7000 (7790) and by Kai-Heng Feng on a newer Dell AOI model. Regards, Hans 1) All In One a monitor with a PC builtin Hans de Goede (2): platform/x86: Add new Dell UART backlight driver tools arch x86: Add dell-uart-backlight-emulator drivers/platform/x86/dell/Kconfig | 15 + drivers/platform/x86/dell/Makefile | 1 + .../platform/x86/dell/dell-uart-backlight.c | 409 ++++++++++++++++++ .../dell-uart-backlight-emulator/.gitignore | 1 + .../x86/dell-uart-backlight-emulator/Makefile | 19 + .../x86/dell-uart-backlight-emulator/README | 46 ++ .../dell-uart-backlight-emulator.c | 166 +++++++ 7 files changed, 657 insertions(+) create mode 100644 drivers/platform/x86/dell/dell-uart-backlight.c create mode 100644 tools/arch/x86/dell-uart-backlight-emulator/.gitignore create mode 100644 tools/arch/x86/dell-uart-backlight-emulator/Makefile create mode 100644 tools/arch/x86/dell-uart-backlight-emulator/README create mode 100644 tools/arch/x86/dell-uart-backlight-emulator/dell-uart-backlight-emulator.c -- 2.44.0
