Message-ID: <d10f7383-1eeb-44d2-a34f-15e76c3451fe@oss.qualcomm.com>
Date: Wed, 19 Nov 2025 10:17:44 +0800
From: Fenglin Wu <fenglin.wu@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: kernel@....qualcomm.com, Lee Jones <lee@...nel.org>,
        Pavel Machek <pavel@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org,
        Subbaraman Narayanamurthy <subbaraman.narayanamurthy@....qualcomm.com>,
        Pavel Machek <pavel@....cz>, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] leds: rgb: leds-qcom-lpg: Don't enable TRILED when
 configuring PWM


On 11/19/2025 12:27 AM, Bjorn Andersson wrote:
> On Tue, Nov 18, 2025 at 10:48:03AM +0800, Fenglin Wu via B4 Relay wrote:
>> From: Fenglin Wu <fenglin.wu@....qualcomm.com>
>>
> Sorry, I didn't find the chance to answer your reply yesterday, and then
> you sent v2, so I'll have to continue the discussion here.
>
>> The PWM signal from the LPG channel can be routed to PMIC GPIOs with
>> proper GPIO configuration, and it is not necessary to enable the
>> TRILED channel in that case. This also applies to the LPG channels
>> that mapped to TRILED channels. Additionally, enabling the TRILED
>> channel unnecessarily would cause a voltage increase in its power
>> supply. Hence remove it.
>>
>> Fixes: 24e2d05d1b68 ("leds: Add driver for Qualcomm LPG")
>> Signed-off-by: Fenglin Wu <fenglin.wu@....qualcomm.com>
>> ---
>> Changes in v2:
>> - Check "chan->in_use" flag in lpg_pwm_apply() is not correct, as it
>>    indicates the channel is being used as a LED and this PWM API would
>>    never get called. Instead, remove the code line which enables TRILED
>>    in lpg_pwm_apply() and update the commit text to explain it clearly.
>>
> I understand that in your case you're routing the PWM signal to a GPIO,
> and in that case the TRILED output should be kept disabled.
>
> But what if I have my load connected to the TRILED and I describe my LPG
> channel as a PWM channel? Is this an invalid use case?
This is not a valid case. If a load (typically an LED) is connected to 
any channel of theTRILED module, it means the LPG channel is used for 
driving an LED, and sub-nodes for the LED devices must be defined. 
Otherwise, the PWM signal will be gated by the TRILED module. Enabling a 
TRILED channel not only opens the PWM gate but also activates an 
internal current sink to manage the load. If you need to output PWM as a 
control signal, for example for fan control, the hardware should connect 
the fan control input to a PMIC GPIO. The PWM signal from an LPG channel 
can be routed there, rather than using a TRILED channel.
> With this patch,
> everything will look like it's working, except silently my signal won't
> come out.
>
> I presume there's no additional configuration on the LPG-side for your
> use case. We just configure the GPIO to tap into the PWM-signal through
> the pinmux settings?
That's correct.
>
> Also, if for some reason the triled was enabled by bootloader, you will
> now leave it enabled forever. This perhaps isn't a big issue though...
In that case, I would assume that the bootloader should also be 
customized to not enabling any LED if there is not a physical LED device 
connected to the TRILED channel.
>
> Perhaps none of this matters in practice, and we should just proceed
> with your approach. If that's the case, then we should at least document
> the behavior.

Does it look good if I push a change in the DT binding document to 
explain this?

--- a/Documentation/devicetree/bindings/leds/leds-qcom-lpg.yaml
+++ b/Documentation/devicetree/bindings/leds/leds-qcom-lpg.yaml
@@ -13,6 +13,10 @@ description: >
    The Qualcomm Light Pulse Generator consists of three different 
hardware blocks;
    a ramp generator with lookup table (LUT), the light pulse generator 
and a three
    channel current sink. These blocks are found in a wide range of 
Qualcomm PMICs.
+  The light pulse generator (LPG) can also be used independently to 
output PWM
+  signal for standard PWM applications. In this scenario, the LPG 
output should
+  be routed to a specific PMIC GPIO by setting the GPIO pin mux to the 
special
+  functions indicated in the datasheet.

  properties:
    compatible:

> Regards,
> Bjorn
>
>> - Link to v1: https://lore.kernel.org/r/20251114-lpg_triled_fix-v1-1-9b239832c53c@oss.qualcomm.com
>> ---
>>   drivers/leds/rgb/leds-qcom-lpg.c | 4 +---
>>   1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
>> index 4f2a178e3d265a2cc88e651d3e2ca6ae3dfac2e2..e197f548cddb03d079c54c4a0f402402c5d047e2 100644
>> --- a/drivers/leds/rgb/leds-qcom-lpg.c
>> +++ b/drivers/leds/rgb/leds-qcom-lpg.c
>> @@ -2,7 +2,7 @@
>>   /*
>>    * Copyright (c) 2017-2022 Linaro Ltd
>>    * Copyright (c) 2010-2012, The Linux Foundation. All rights reserved.
>> - * Copyright (c) 2023-2024, Qualcomm Innovation Center, Inc. All rights reserved.
>> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
>>    */
>>   #include <linux/bits.h>
>>   #include <linux/bitfield.h>
>> @@ -1247,8 +1247,6 @@ static int lpg_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>>   
>>   	lpg_apply(chan);
>>   
>> -	triled_set(lpg, chan->triled_mask, chan->enabled ? chan->triled_mask : 0);
>> -
>>   out_unlock:
>>   	mutex_unlock(&lpg->lock);
>>   
>>
>> ---
>> base-commit: ea1c4c7e648d1ca91577071fc42fdc219521098c
>> change-id: 20251114-lpg_triled_fix-44491b49b340
>>
>> Best regards,
>> -- 
>> Fenglin Wu <fenglin.wu@....qualcomm.com>
>>
>>

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