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 5480 AIO has an ACPI device for one if its UARTs with the above _HID + _CID. Loading the dell-uart-backlight driver fails with the following errors:

[ 18.261353] dell_uart_backlight serial0-0: Timed out waiting for response. [ 18.261356] dell_uart_backlight serial0-0: error -ETIMEDOUT: getting firmware version [ 18.261359] dell_uart_backlight serial0-0: probe with driver dell_uart_backlight failed with error -110

Indicating that there is no backlight controller board attached to the UART, while 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: cd8e468efb4f ("ACPI: video: Add Dell UART backlight controller detection") Cc: All applicable stable@vger.kernel.org Signed-off-by: Hans de Goede hdegoede@redhat.com --- drivers/acpi/video_detect.c | 9 +++++++++ 1 file changed, 9 insertions(+)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c index b70e84e8049a..015bd8e66c1c 100644 --- a/drivers/acpi/video_detect.c +++ b/drivers/acpi/video_detect.c @@ -844,6 +844,15 @@ static const struct dmi_system_id video_detect_dmi_table[] = { * controller board in their ACPI tables (and may even have one), but * which need native backlight control nevertheless. */ + { + /* https://github.com/zabbly/linux/issues/26 */ + .callback = video_detect_force_native, + /* Dell OptiPlex 5480 AIO */ + .matches = { + DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."), + DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 5480 AIO"), + }, + }, { /* https://bugzilla.redhat.com/show_bug.cgi?id=2303936 */ .callback = video_detect_force_native,