Re: [RFC PATCH 0/2] leds: Add optional instance identifier for deterministic naming

Jacek Anaszewski
2025-12-29T14:28:26Z

On 12/29/25 13:30, Andriy Shevencho wrote:
> On Mon, Dec 29, 2025 at 12:16:17PM +0100, Jacek Anaszewski wrote:
>> On 12/28/25 19:22, Jonathan Brophy wrote:
>
>>> This patch series introduces an optional "led-instance" device tree property
>>> to address non-deterministic LED naming when multiple LEDs share the same
>>> function and color.
>>>
>>> Currently, the LED core appends numerical suffixes (_1, _2, etc.) based on
>>> registration order when duplicate function:color combinations exist. This
>>> creates several problems:
>>>
>>> 1. **Non-deterministic naming**: Registration order determines suffix values,
>>> which can change across boots due to probe ordering, async initialization,
>>> or module load order.
>>>
>>> 2. **Non-semantic identifiers**: Names like "lan:green_23" provide no
>>> indication of which physical LED or subsystem they represent.
>>>
>>> 3. **Breaks userspace automation**: Network management tools, LED control
>>> daemons, and hardware monitoring cannot reliably identify LEDs.
>>>
>>> 4. **Ambiguous numbering**: "lan:green_23" could be mistaken for LAN port 23
>>> when it may actually be the 23rd registered LED of any port.
>>>
>>> 5. **Namespace pollution**: The alternative of adding vendor-specific function
>>> names (LED_FUNCTION_LAN_PORT0, LED_FUNCTION_LAN_PORT1...) pollutes the
>>> function namespace. The instance identifier keeps standard functions clean
>>> while allowing contextual differentiation.
>>>
>>> 6. **Breaks naming convention**: The _1, _2 suffix was intended only as a
>>> collision avoidance workaround, but has become the de facto standard for
>>> hardware with multiple identical LEDs.
>>>
>>> **Example: 48-port network switch**
>>>
>>> Current behavior (non-deterministic):
>>> /sys/class/leds/lan:green ← Port 0? Unknown
>>> /sys/class/leds/lan:green_1 ← Could be any port
>>> /sys/class/leds/lan:green_2 ← Could be any port
>>> ...
>>> /sys/class/leds/lan:green_47 ← Could be port 1 due to probe order
>>>
>>> Proposed behavior (deterministic):
>>> /sys/class/leds/lan:green:port0 ← Always port 0
>>> /sys/class/leds/lan:green:port1 ← Always port 1
>>> /sys/class/leds/lan:green:port2 ← Always port 2
>>> ...
>>> /sys/class/leds/lan:green:port47 ← Always port 47
>>>
>>> **Example: Multi-domain power indicators**
>>>
>>> Current behavior (non-deterministic):
>>> /sys/class/leds/power:red ← Which power source?
>>> /sys/class/leds/power:red_1 ← Which power source?
>>> /sys/class/leds/power:red_2 ← Which power source?
>>>
>>> Proposed behavior (deterministic):
>>> /sys/class/leds/power:red:mains ← Mains power indicator
>>> /sys/class/leds/power:red:battery ← Battery power indicator
>>> /sys/class/leds/power:red:usb ← USB power indicator
>>>
>>> **Design principles:**
>>>
>>> - Backward compatible: Instance identifier is optional
>>> - Extends existing convention: function:color becomes function:color:instance
>>> - Follows kernel precedent: Similar to eth0/eth1, gpio0/gpio1 naming patterns
>>> - Ignored with deprecated "label" property: Avoids conflicts with legacy code
>>>
>>> **Alternative solutions considered:**
>>>
>>> 1. function-enumerator: Only supports numbers (0, 1, 2), producing names like
>>> "lan:green-0" which are still non-semantic. The 48-port switch needs "port0"
>>> to match physical port labels.
>>
>> I think that we have currently everything in place to address the issue
>> you're trying to solve with this patch. Just introduce dedicated
>> function like LAN_PORT, and exploit function-enumerator.
>
> The problem as I understood not exactly in this. The reporter wants
> deterministic way of the mapping between HW numbered LEDs and their respective
> names. It seems it was already mentioned that current code depends on the
> arbitrary probe ordering. Saying this, I now think that perhaps GPIO led driver
> should somehow allocate a range of the LEDs and then enumerate them in
> accordance with the DT description?

function-enumerator DT property enables deterministic enumeration.

--
Best regards,
Jacek Anaszewski