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

[Fenglin Wu]

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@xxxxxxxxxxx>
> >
> > 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,