linux-kernel - Re: [PATCH] arm64: dts: qcom: hamoa-iot-evk: enable pwm rgb leds

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Message-ID: <297c10fc-9b36-4eae-8a56-7556cc14b8c6@oss.qualcomm.com>
Date: Tue, 21 Oct 2025 11:47:43 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Tingguo Cheng <tingguo.cheng@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc: kernel@....qualcomm.com, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kamal Wadhwa <kamal.wadhwa@....qualcomm.com>,
        Rakesh Kota <rakesh.kota@....qualcomm.com>,
        Fenglin Wu <fenglin.wu@....qualcomm.com>
Subject: Re: [PATCH] arm64: dts: qcom: hamoa-iot-evk: enable pwm rgb leds

On 10/21/25 8:29 AM, Tingguo Cheng wrote:
> 
> On 10/17/2025 4:09 PM, Konrad Dybcio wrote:
>> On 10/17/25 10:06 AM, Tingguo Cheng wrote:
>>> Add red, green and blue LED channels for the RGB device connected to
>>> PMC8380C PWM-LED pins.
>>>
>>> Signed-off-by: Tingguo Cheng<tingguo.cheng@....qualcomm.com>
>>> ---
>> Just to make sure, is this a "multicolor LED" consisting of 3 ones,
>> and *not* three LEDs that are supposed to communicate different
>> functions (i.e. network, power, disk i/o)?
> Yes, it's a multicolor LED composed of three individual LEDs within a single package—not three separate LEDs for different functions like network, power, or disk I/O.
> However, there's one exception worth mentioning:
> The blue channel is connected to two sourcing signals—the EDL indicator and the PMIC PWM-RGB blue LED—via two resistors. These resistors allow selection between the two sources.
> By default, the board is configured with the resistor soldered to connect the blue LED to the EDL indicator.
> To support software control, I’ve added the blue channel in the DTS, enabling the capability to light the blue LED from the software side.
> Some developers may choose to re-solder the resistor to connect the blue LED to the PMIC PWM-RGB output instead, depending on their hardware setup.

Ehhh didn't know we had to save money on onboard LEDs..

This is really inconvenient to handle in software, because if e.g.
userspace configures RGB=0/0/255 to signal a notification, Linux
may program the light pulse generator, but the user will never
receive it. On the flip side, not describing it here will not let
anyone use it.. I'm not sure which way is worse

Konrad