linux-kernel - Re: [PATCH RESEND v3] leds: flash: leds-qcom-flash: limit LED current based on thermal condition

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Message-ID: <40dfeb9c-e420-4695-939f-ef9b1985d61c@quicinc.com>
Date: Mon, 8 Jul 2024 10:59:31 +0800
From: Fenglin Wu <quic_fenglinw@...cinc.com>
To: Luca Weiss <luca.weiss@...rphone.com>, <kernel@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>, Pavel Machek <pavel@....cz>,
        Lee Jones
	<lee@...nel.org>
CC: <linux-leds@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "David
 Collins" <quic_collinsd@...cinc.com>,
        Subbaraman Narayanamurthy
	<quic_subbaram@...cinc.com>
Subject: Re: [PATCH RESEND v3] leds: flash: leds-qcom-flash: limit LED current
 based on thermal condition

On 7/5/2024 10:23 PM, Luca Weiss wrote:
> On Fri Jul 5, 2024 at 9:55 AM CEST, Fenglin Wu via B4 Relay wrote:
>> From: Fenglin Wu <quic_fenglinw@...cinc.com>
>>
>> The flash module has status bits to indicate different thermal
>> conditions which are called as OTSTx. For each OTSTx status,
>> there is a recommended total flash current for all channels to
>> prevent the flash module entering into higher thermal level.
>> For example, the total flash current should be limited to 1000mA/500mA
>> respectively when the HW reaches the OTST1/OTST2 thermal level.
> 
> Hi Fenglin,
> 
> Only semi-related to this patch, but I wanted to ask.
> 
> Since most phones with a flash also have a thermistor for the flash led,
> is there any plan to add support to be able to declare the flash led to
> be a "cooling-device" for the relevant thermal zone? That way from a
> Linux thermal API standpoint when the zone gets too hot that it can ask
> the driver to throttle the brightness or turn the LED off completely.
> 
> Right now the only action the kernel can take is with type 'critical' to
> just kill the entire system to mitigate the thermal situation.
> 
> Regards
> Luca
> 

Hi Luca,

This change provides the ability to throttle flash current based on the 
thermal status sensed by the temperature sensor inside the flash module 
HW , it doesn't need to register anything in Linux thermal framework.

For the case that you mentioned, when an external thermistor is 
installed nearby the flash LED component and normally the ADC_TM driver 
registers a thermal_zone device with it, I agree that having the flash 
LED driver providing a thermal_cooling device so that any cooling 
mapping policy could be defined between the thermal sensor and the 
cooling device would be a good option for better system level thermal 
control. I would assume that this could be added in flash LED framework 
driver instead of the client drivers considering this should be a common 
request because of the big thermal dissipation of flash LED?

Fenglin
>>
>> ---
>> base-commit: ca66b10a11da3c445c9c0ca1184f549bbe9061f2
>> change-id: 20240507-qcom_flash_thermal_derating-260b1f3c757c
>>
>> Best regards,
>