linux-kernel - Re: AW: [PATCH v2 1/4] leds: lp50xx: add setting of default intensity from DT

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Date:   Sat, 6 Feb 2021 21:58:39 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Sven Schuchmann <schuchmann@...leissheimer.de>,
        Pavel Machek <pavel@....cz>
Cc:     Dan Murphy <dmurphy@...com>, Rob Herring <robh+dt@...nel.org>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: AW: [PATCH v2 1/4] leds: lp50xx: add setting of default intensity
 from DT

Sven,

On 2/6/21 2:14 PM, Sven Schuchmann wrote:
> Hello Dan,
> 
>> Von: Jacek Anaszewski <jacek.anaszewski@...il.com>
>> Gesendet: Freitag, 5. Februar 2021 19:37
>> Hi Pavel,
>>
>> On 2/5/21 11:23 AM, Pavel Machek wrote:
>>> Hi!
>>>
>>>>>>        patternProperties:
>>>>>>          "(^led-[0-9a-f]$|led)":
>>>>>> @@ -99,6 +104,7 @@ examples:
>>>>>>                   reg = <0x1>;
>>>>>>                   color = <LED_COLOR_ID_RGB>;
>>>>>>                   function = LED_FUNCTION_CHARGING;
>>>>>> +               default-intensity = <100 0 0>;
>>
>> How will you know which array position is for which child LED?
>> I presume DT child nodes are not guaranteed to be parsed in the order
>> of declaration?
> 
> I tried to fiddle this out, but it seems Jacek is right over here.
> The multi-led definition looks like this (from the documentation leds-lp50xx.yaml)
> 
>          multi-led@1 {
>                 #address-cells = <1>;
>                 #size-cells = <0>;
>                 reg = <0x1>;
>                 color = <LED_COLOR_ID_RGB>;
>                 function = LED_FUNCTION_CHARGING;
> 
>                 led-0 {
>                     color = <LED_COLOR_ID_RED>;
>                 };
> 
>                 led-1 {
>                     color = <LED_COLOR_ID_GREEN>;
>                 };
> 
>                 led-2 {
>                     color = <LED_COLOR_ID_BLUE>;
>                 };
>            };
> 
> But it seems that the color definition of each led is ignored.
> By ignored I mean the driver does not take care which color
> is at which position. So if I change led-0 to be LED_COLOR_ID_BLUE
> and led-2 to be LED_COLOR_ID_RED nothing will change if I write
> from userspace. Could you help to clarify?
> Then it is even hard to know which led to set with default-intensity.

See Documentation/ABI/testing/sysfs-class-led-multicolor and
documentation of multi_index and multi_intensity files.
It is the multi_index file that tells what is the order of colors
in the multi_intensity file.

And that depends on the order of enumeration of the nodes by DT parser.

> Also it seems that the enumeration of the multi-leds should
> start with multi-led@0 (and not 1 as in the documentation).

The @unit-address part of node name must match the first address
specified in the reg property of the node, so this is correct.
-- 
Best regards,
Jacek Anaszewski