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

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Message-ID: <aVF3ZTxqSXWVcCVN@smile.fi.intel.com>
Date: Sun, 28 Dec 2025 20:31:01 +0200
From: Andriy Shevencho <andriy.shevchenko@...ux.intel.com>
To: Jonathan Brophy <professorjonny98@...il.com>
Cc: lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>,
	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>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-leds@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] leds: Add optional instance identifier for
 deterministic naming

On Mon, Dec 29, 2025 at 07:22:43AM +1300, Jonathan Brophy wrote:
> 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

Hmm... I think the research missed the udev + sysfs approach as done for the
networking devices. Hence the question: do we have enough data in sysfs for
leds to understand their HW connections / semantics?

-- 
With Best Regards,
Andy Shevchenko