Dell All In One (AIO) models released after 2017 may use a backlight controller board connected to an UART.

In DSDT this uart port will be defined as:

Name (_HID, "DELL0501") Name (_CID, EisaId ("PNP0501")

The Dell OptiPlex 7760 AIO has an ACPI device for one if its UARTs with the above _HID + _CID. Loading the dell-uart-backlight driver shows that there actually is a backlight controller board attached to the UART, which reports a firmware version of "G&MX01-V15".

But the backlight controller board does not actually control the backlight brightness and the GPU's native backlight control method does work.

Add a quirk to use the GPU's native backlight control method on this model.

Fixes: 484bae9e4d6a ("platform/x86: Add new Dell UART backlight driver") Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2303936 Cc: stable@vger.kernel.org Signed-off-by: Hans de Goede hdegoede@redhat.com --- drivers/acpi/video_detect.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c index e509dcbf3090..674b9db7a1ef 100644 --- a/drivers/acpi/video_detect.c +++ b/drivers/acpi/video_detect.c @@ -823,6 +823,21 @@ static const struct dmi_system_id video_detect_dmi_table[] = { }, },

+ /* + * Dell AIO (All in Ones) which advertise an UART attached backlight + * controller board in their ACPI tables (and may even have one), but + * which need native backlight control nevertheless. + */ + { + /* https://bugzilla.redhat.com/show_bug.cgi?id=2303936 */ + .callback = video_detect_force_native, + /* Dell OptiPlex 7760 AIO */ + .matches = { + DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."), + DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 7760 AIO"), + }, + }, + /* * Models which have nvidia-ec-wmi support, but should not use it. * Note this indicates a likely firmware bug on these models and should