linux-kernel - Re: [PATCH RFC] leds: leds-lp50xx: Handle reg to get correct multi

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Message-ID:
 <PAWPR02MB9281789F85D773CEC278688F9B96A@PAWPR02MB9281.eurprd02.prod.outlook.com>
Date: Tue, 13 May 2025 13:04:24 +0000
From: Johan Adolfsson <Johan.Adolfsson@...s.com>
To: Jacek Anaszewski <jacek.anaszewski@...il.com>, Lee Jones <lee@...nel.org>,
	Pavel Machek <pavel@...nel.org>
CC: "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Kernel
	<Kernel@...s.com>, Johan Adolfsson <Johan.Adolfsson@...s.com>
Subject: Re: [PATCH RFC] leds: leds-lp50xx: Handle reg to get correct
 multi_index


Hi Jacek,

>From: Jacek Anaszewski <jacek.anaszewski@...il.com>
>Sent: Monday, May 12, 2025 20:10
>To: Johan Adolfsson; Lee Jones; Pavel Machek
>Cc: linux-leds@...r.kernel.org; linux-kernel@...r.kernel.org; Kernel
>Subject: Re: [PATCH RFC] leds: leds-lp50xx: Handle reg to get correct multi_index
>
>On 5/12/25 12:59, Johan Adolfsson wrote:
>>
>> From: Jacek Anaszewski <jacek.anaszewski@...il.com>
>> Sent: Saturday, May 10, 2025 17:32
>> To: Johan Adolfsson; Lee Jones; Pavel Machek
>> Cc: linux-leds@...r.kernel.org; linux-kernel@...r.kernel.org; Kernel
>> Subject: Re: [PATCH RFC] leds: leds-lp50xx: Handle reg to get correct multi_index
>>
>>> Hi Johan,
>>>
>>> On 5/6/25 12:39, Johan Adolfsson wrote:
>>>> mc_subled used for multi_index needs well defined array indexes,
>>>> to guarantee the desired result, optionally use reg for that.
>>>>
>>>> If devicetree child nodes is processed in random or reverse order
>>>> you may end up with multi_index "blue green red" instead of the expected
>>>> "red green blue".
>>>> If user space apps uses multi_index to deduce how to control the leds
>>>> they would most likely be broken without this patch if devicetree
>>>> processing is reversed (which it appears to be).
>>>
>>> Are you trying to solve some real problem that occurred to you?
>>
>> Yes! Since the subled is indexed by the processing order, it gets reversed if devicetree processing is reversed
>> (which I understand is a "feature"), so instead of "red green blue" I would get "blue green red" in the multi_index file without this patch.
>> The mapping to the hardware does not match that, so writing "255 0 0" to multi_intensity will give me red and not blue.

>You are expected to write intensities to the multi_intensity file
>according to the order of colors listed in multi_index file.

That is what I did above, but LED turned red and not blue.

>>> The order of DT nodes parsing is not a problem here - we save
>>> color index in subled_info to be able to figure out which color
>>> is on which position. This information can be retrieved in sysfs
>>> by reading multi_index file.
>>
>> Maybe the bug is somewhere else in the leds-lp50xx if that is supposed to work,
>> but I still think it's a good thing to be able to get the expected order in the multi_index file.
>
>Please make sure you read Documentation/leds/leds-class-multicolor.rst.
>There is no such term as "expected order in the multi_index file".
>The framework is called multicolor, not rgb. The order of colors does
>not need to be RGB.

Maybe I'm missing something here - but how do i specify that a certain pin on the driver IC is connected to a certain color of the LED.
The devicetree looks like this:
It seems the first number in multi_intensity seem to go to pin regardless of what multi_index says.

			multi-led@0 {
				reg = <0x0>;
				color = <LED_COLOR_ID_RGB>;
				label = "led:rgb";
				function = "led";
				linux,default-trigger = "default-on";
				max-brightness = <255>;
				#address-cells = <1>;
				#size-cells = <0>;

				/* Need BLUE GREEN RED here or reg to give red green blue in multi_index! */
				led-0@0 {
					color = <LED_COLOR_ID_RED>;
					reg = <0>;
				};

				led-1@1 {
					color = <LED_COLOR_ID_GREEN>;
					reg = <1>;
				};

				led-2@2 {
					color = <LED_COLOR_ID_BLUE>;
					reg = <4>;
				};
			};


>--
>Best regards,
>Jacek Anaszewski

Best regards
/Johan