From: Val Packett <val@packett.cool>
To: Avalon Vargas Centeno <avalon.vargas.centeno@est.una.ac.cr>,
linux-arm-msm@vger.kernel.org
Cc: andersson@kernel.org, konradybcio@kernel.org,
devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org,
neil.armstrong@linaro.org, bryan.odonoghue@linaro.org
Subject: Re: [RFC] Dell Inspiron 7441 AUO0BA4 panel backlight: PWM configuration
Date: Fri, 11 Sep 2026 22:00:33 -0300 [thread overview]
Message-ID: <0049ee8a-d9b2-4692-9494-5a8f054accaa@packett.cool> (raw)
In-Reply-To: <CAGXpr54Bn9Wf24asY2RcXgBNLy1A16=U1mtFx7mKeNK4CCOCYQ@mail.gmail.com>
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
prev parent reply other threads:[~2026-09-12 1:00 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-11 22:11 [RFC] Dell Inspiron 7441 AUO0BA4 panel backlight: PWM configuration Avalon Vargas Centeno
2026-09-12 1:00 ` Val Packett [this message]
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