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

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Message-ID: <20251228182252.1550173-1-professorjonny98@gmail.com>
Date: Mon, 29 Dec 2025 07:22:43 +1300
From: Jonathan Brophy <professorjonny98@...il.com>
To: lee Jones <lee@...nel.org>,
	Pavel Machek <pavel@...nel.org>,
	Andriy Shevencho <andriy.shevchenko@...ux.intel.com>,
	Jonathan Brophy <professor_jonny@...mail.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Radoslav Tsvetkov <rtsvetkov@...dotech.eu>
Cc: devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-leds@...r.kernel.org
Subject: [RFC PATCH 0/2] leds: Add optional instance identifier for deterministic naming

From: Jonathan Brophy <professor_jonny@...mail.com>

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.

2. Deprecated "label" property: Being actively removed from LED bindings. New
   code should not rely on deprecated APIs.

3. Different function names: LED_FUNCTION_LAN_PORT0, LED_FUNCTION_LAN_PORT1...
   This pollutes the function namespace with hardware-specific combinations.

This RFC seeks feedback on:
- Property naming: "led-instance" vs "led-subsystem" vs "led-context"
- Implementation approach
- Additional use cases to document

Jonathan Brophy (2):
  leds: core: Add support for led-instance property
  dt-bindings: leds: common: Add led-instance property

 .../devicetree/bindings/leds/common.yaml      | 93 +++++++++++++++++++
 drivers/leds/led-core.c                       | 43 +++++++--
 2 files changed, 126 insertions(+), 10 deletions(-)

--
2.43.0