On 9/11/26 7:11 PM, Avalon Vargas Centeno wrote:
Hello, On my Dell Inspiron 14 Plus 7441 (BIOS 2.16.0, aarch64 Linux 7.2.4, NixOS), the AUO B140QAX01.H / AUO0BA4 panel originally exposed an unusable dp_aux_backlight with max_brightness 0. GNOME could not adjust brightness. Panel DPCD bytes at 0x700-0x72f: 05 9b 91 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 0a 04 0a 00 1b 00 0d 2f 03 ff ff 03 The capability bits indicate PWM brightness setting rather than AUX brightness setting. Inspection of the local panel-edp and DP helper code suggests that this capability combination can leave the AUX backlight maximum at zero. This is a code-path inference, not a separately verified generic DRM driver bug. [..]
Weird. I know someone who has a B140QAX01.H in a 7445 (that's how I've added it to edp_panels) and they did not have that problem, aux backlight worked fine…
panel-edp does not seem to care about DPCD indicating PWM; if the brightness property is present in the device tree it *will* be used, and AUX is used as a fallback if the external DT-provided brightness was absent. If we really need to support this (without adding more devicetrees), I guess we could add some opt-in prefer-aux-brightness thing..
~val
