linux-kernel - Re: [PATCH 3/3] arm64: dts: qcom: sm7225-fairphone-fp4: configure flash LED

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Date:   Thu, 5 Jan 2023 11:30:04 +0800
From:   Fenglin Wu <quic_fenglinw@...cinc.com>
To:     Luca Weiss <luca.weiss@...rphone.com>, Pavel Machek <pavel@....cz>
CC:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-leds@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] arm64: dts: qcom: sm7225-fairphone-fp4: configure
 flash LED



On 2022/12/12 21:59, Luca Weiss wrote:
> On Sat Dec 10, 2022 at 6:16 PM CET, Pavel Machek wrote:
>> Hi!
>>
>>> Configure the pm6150l flash node for the dual flash LEDs found on FP4.
>>
>>> +&pm6150l_flash {
>>> +	status = "okay";
>>> +
>>> +	led-0 {
>>> +		function = LED_FUNCTION_FLASH;
>>> +		color = <LED_COLOR_ID_YELLOW>;
>>> +		led-sources = <1>;
>>> +		led-max-microamp = <180000>;
>>> +		flash-max-microamp = <1000000>;
>>> +		flash-max-timeout-us = <1280000>;
>>> +	};
> 
> Hi Pavel,
> 
>>
>> I'm pretty sure the flash is not yellow.
> 
> The marketing term is Dual LED flash or Dual-tone flash, one LED is a
> blue-ish white and one is a yellow-ish white, but from what I can tell,
> in the original code it's always referred to as white and yellow so I
> also followed that here.
> 
> Also the LEDs are right next to each other so in practise for torch just
> both go on, and for camera flash I cannot really tell you but I guess
> it's doing something there with the camera tuning.
> 
> See also this picture:
> https://shop.fairphone.com/media/catalog/product/cache/b752d78484639b19641a8560800d919d/p/_/p_5b_main_camera_back.jpg
> 
Hi Pavel,

Luca is right. It is normally called dual CCT (Correlated Color 
Temperature) flash LED. It has 2 LEDs, one is with higher CCT (~6000K) 
so it looks like a white LED, another is with lower CCT (~2000K) and it 
looks like a yellow LED. I am not an expert of this but my understanding 
is the camera tuning process normally adjusts the brightness of the two 
LEDs and enables them to get different CCT for different snapshots.
I was thinking to use the "white" and "yellow" to name the flash LEDs 
which should be much better that just using indexes, it implicitly tell 
that the "white" one is having higher CCT and the "yellow" one is having 
lower CCT.

Fenglin
>>
>> Plus, how is the node in /sys/class/leds called? Can you make an entry
>> in Documentation/leds/well-known-leds.txt and ensure the name stays
>> consistent across devices?
> 
> / # ls -al /sys/class/leds/white:flash/
> total 0
> drwxr-xr-x    3 0        0                0 Jan  1 00:00 .
> drwxr-xr-x    4 0        0                0 Jan  1 00:00 ..
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 brightness
> lrwxrwxrwx    1 0        0                0 Jan  1 00:00 device -> ../../../c440000.spmi:pmic@5:led-controller@...0
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 flash_brightness
> -r--r--r--    1 0        0             4096 Jan  1 00:00 flash_fault
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 flash_strobe
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 flash_timeout
> -r--r--r--    1 0        0             4096 Jan  1 00:00 max_brightness
> -r--r--r--    1 0        0             4096 Jan  1 00:00 max_flash_brightness
> -r--r--r--    1 0        0             4096 Jan  1 00:00 max_flash_timeout
> drwxr-xr-x    2 0        0                0 Jan  1 00:00 power
> lrwxrwxrwx    1 0        0                0 Jan  1 00:00 subsystem -> ../../../../../../../../../class/leds
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 uevent
> / # ls -al /sys/class/leds/yellow:flash/
> total 0
> drwxr-xr-x    3 0        0                0 Jan  1 00:00 .
> drwxr-xr-x    4 0        0                0 Jan  1 00:00 ..
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 brightness
> lrwxrwxrwx    1 0        0                0 Jan  1 00:00 device -> ../../../c440000.spmi:pmic@5:led-controller@...0
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 flash_brightness
> -r--r--r--    1 0        0             4096 Jan  1 00:00 flash_fault
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 flash_strobe
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 flash_timeout
> -r--r--r--    1 0        0             4096 Jan  1 00:00 max_brightness
> -r--r--r--    1 0        0             4096 Jan  1 00:00 max_flash_brightness
> -r--r--r--    1 0        0             4096 Jan  1 00:00 max_flash_timeout
> drwxr-xr-x    2 0        0                0 Jan  1 00:00 power
> lrwxrwxrwx    1 0        0                0 Jan  1 00:00 subsystem -> ../../../../../../../../../class/leds
> -rw-r--r--    1 0        0             4096 Jan  1 00:00 uevent
> 
> There's also already flash LED on PinePhone and some MSM8916 devices,
> but I think they also have white:flash based on the dt.
> 
>>
>> Best regards,
>> 								Pavel
>> -- 
>> People of Russia, stop Putin before his war on Ukraine escalates.
>