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

Andriy Shevencho
2025-12-29T14:45:06Z

On Mon, Dec 29, 2025 at 03:28:20PM +0100, Jacek Anaszewski wrote:
> 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.

Ah, that's nice!

--
With Best Regards,
Andy Shevchenko