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

From: Jacek Anaszewski <jacek.anaszewski@gmail.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: linux-leds@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, robh@kernel.org,
	Baolin Wang <baolin.wang@linaro.org>,
	Daniel Mack <daniel@zonque.org>, Dan Murphy <dmurphy@ti.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Oleh Kravchenko <oleg@kaa.org.ua>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Simon Shields <simon@lineageos.org>,
	Xiaotong Lu <xiaotong.lu@spreadtrum.com>
Subject: Re: [PATCH 02/24] leds: core: Add support for composing LED class device names
Date: Mon, 12 Nov 2018 17:01:59 +0100	[thread overview]
Message-ID: <662c02ba-455b-e2bf-a5e2-ae3933161894@gmail.com> (raw)
In-Reply-To: <20181112103513.GB5695@amd>

Hi,

On 11/12/2018 11:35 AM, Pavel Machek wrote:
> Hi!
> 
>>>> 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.
> 
> I agree that removing it is "just too drastic".
> 
> But it is not just for backwards compatibility. See my examples above,
> it is needed to tell which device the LED is asociated with, and it is
> absolutely required for USB devices (for example).

For USB devices there is already ledtrig-usbport available, which
provides sysfs interface for defining and reading the usb ports,
the status of which the LED indicates. Since the USB devices can be
attached/removed dynamically, it would be impossible to reflect
the associations in the LED class device name.

> And even for "embedded" stuff like routers, we want eth0:green:link,
> eth0:yellow:activity and not some kind of hack.

eth0 is not something you can be certain of at the stage of defining DT
node.

> Ideally, colors would come from fixed list, functions would come from
> fixed list, and device part would come from name used elsewhere in the
> kernel.
> 
> (And yes, it probably means we should have something in device tree to
> link LED to its device. device = "name" would be good start...)

Why would you need such link?

-- 
Best regards,
Jacek Anaszewski