linux-kernel - Re: [PATCH 02/24] leds: core: Add support for composing LED class device names

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Message-ID: <e72ac342-5253-851a-e54f-b1bd752be628@gmail.com>
Date:   Mon, 12 Nov 2018 02:01:59 +0200
From:   Vesa Jääskeläinen <dachaac@...il.com>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>
Cc:     linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, robh@...nel.org,
        Baolin Wang <baolin.wang@...aro.org>,
        Daniel Mack <daniel@...que.org>, Dan Murphy <dmurphy@...com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Oleh Kravchenko <oleg@....org.ua>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Simon Shields <simon@...eageos.org>,
        Xiaotong Lu <xiaotong.lu@...eadtrum.com>
Subject: Re: [PATCH 02/24] leds: core: Add support for composing LED class
 device names

Hi,

On 11/11/2018 23.14, Jacek Anaszewski wrote:
> On 11/11/2018 09:16 PM, Pavel Machek wrote:
>> Hi!
>>
>>>>> diff --git a/Documentation/leds/leds-class.txt b/Documentation/leds/leds-class.txt
>>>>> index 836cb16..e9009c4 100644
>>>>> --- a/Documentation/leds/leds-class.txt
>>>>> +++ b/Documentation/leds/leds-class.txt
>>>>> @@ -43,7 +43,7 @@ LED Device Naming
>>>>>   
>>>>>   Is currently of the form:
>>>>>   
>>>>> -"devicename:colour:function"
>>>>> +"colour:function"

Couldn't we have here multiple variants that would then be chosen based 
on device tree definition?

"devicename:colour:function"
"devicename:function"
"devicename:label"
"colour:function"
"function"
"label"

If "label" would be specified then just use that as a led name, giving name:
- label

If "function" would be defined then go to special formatting with 
optional "color", giving names:
- color:function
- function

I suppose 'devicename' would then be automatically filled based on 
driver instance unless one defines 'no-devicename' or something like 
that for led definition.

Personally I do not see the need for "color" in any led name. In my 
opinion the only thing needed here would be location prefix (where 
needed -- and it should be possible to disable that) and then logical 
name for the led.

>>>> I don't think we want to do it in all cases.
>>>>
>>>> So, on my cellphone seeing lp5523:green:led is indeed not useful.
>>>>
>>>> But on notebook with usb keyboard attached, you need to keep the
>>>> devicename to be able to distinguish capslock on internal keyboard and
>>>> capslock on first USB keyboard and capslock on second USB keyboard.
>>>>
>>>> Taking look at the list of functions, here's stuff like "hdd" and
>>>> "hdderr". I assume the first means hdd activity... If we can do it, it
>>>> would be nicest to have "sda:green:activity" and maybe
>>>> "sda:red:error". For a raid array with 8 drives...
>>>>
>>>> For example I have a router running linux. It has 4 lan ports, with
>>>> correspondings LED, and an wan led.
>>>>
>>>> Having "green:lan1" to "green:lan4" and "green:wan" plus
>>>> "red:wanerror" would work, but I'd really preffer
>>>> "eth0:green:link"... "adsl0:green:link", "adsl0:red:error".
>>>>
>>>> There are now phones with flashes on both main and selfie
>>>> cameras. Again, knowing which device is which is important. As is
>>>> knowing which display is controlled by particular backlight.
>>>
>>> It's overcomplicating the naming again. In every case you can tweak
>>> the function name to eth0_link, eth1_link etc.
>>
>> Well, but in such case it would be good to keep existing scheme.
>>
>> My system looks like this:
>>
>> input16::capslock    tpacpi::bay_active    tpacpi::standby
>> input16::numlock     tpacpi::dock_active   tpacpi::thinklight
>> input16::scrolllock  tpacpi::dock_batt	      tpacpi::thinkvantage
>> input5::capslock     tpacpi::dock_status1  tpacpi::unknown_led
>> input5::numlock      tpacpi::dock_status2  tpacpi::unknown_led2
>> input5::scrolllock   tpacpi:green:batt	      tpacpi::unknown_led3
>>
>> I agree that we should get rid of "tpacpi:" part in some cases. But
>> it does not make sense to get rid of "input16:" part -- it tells you
>> if the LED is on USB or on built-in keyboard.
>>
>> Ideally, tpacpi::thinklight would be input5::frontlight (as it is
>> frontlight for the keyboard).
>>
>> Yes we should simplify, but it still needs to work in all cases.
> 
> Well, label is not being removed. You still can use it an the old
> fashion, even when using new led_compose_name().
> 
> Maybe removing the description of the old LED naming from
> Documentation/leds/leds-class.txt was too drastic move.
> I'll keep it next to the new one, and only add a note that
> it is kept only for backwards compatibility.

With above proposal for naming it should match more or less everyone's 
needs?

Simple naming for embedded device makers and more advanced for server 
system makers.

No need to say that something is legacy or backwards compatibility feature.

Thanks,
Vesa Jääskeläinen