Hi Alexander,
On 5/16/25 09:35, Alexander Dahl wrote:
Hei hei,
just wanted to create a new thread on a similar topic, but this is so
close, just hooking in here …
Am Sat, May 10, 2025 at 02:43:45PM +0200 schrieb Jacek Anaszewski:
Hi all,
On 5/8/25 15:49, Lee Jones wrote:
On Thu, 08 May 2025, Wolfram Sang wrote:
On Thu, Apr 17, 2025 at 01:39:14PM +0200, Geert Uytterhoeven wrote:
Hi Wolfram,
CC leds
On Thu, 17 Apr 2025 at 11:33, Wolfram Sang
<wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote:
Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
---
Changes since v2:
* using function, color, function-enumerator properties now
Honestly, this is better than using node names? With V2, the LEDs were
named as in the schematics, now they are called:
lrwxrwxrwx 1 root root 0 May 12 12:10 green:programming-0 -> ../../devices/platform/leds/leds/green:programming-0
lrwxrwxrwx 1 root root 0 May 12 12:10 green:programming-1 -> ../../devices/platform/leds/leds/green:programming-1
lrwxrwxrwx 1 root root 0 May 12 12:10 green:programming-2 -> ../../devices/platform/leds/leds/green:programming-2
...
Which gets even more confusing if we might later add LEDs not on this
board, but on the expansion board. 'green:programming-8' sits where?
I really wonder, but if this is the official way now...
Good point! So I'm inclined to take v2...
Let's raise this with the LED people. I don't want to fight Pavel when
v2 hits the CiP tree ;-)
So, if there is no other opinion here, can we remove function, color,
function-enumerator and just use the node names which match the
schematics? Basically apply V2?
I didn't author the semantics nor the rules surrounding them, but I am
obliged to enforce them. Therefore "LED people" say, please stick to
convention as stated in the present documentation:
https://docs.kernel.org/leds/leds-class.html#led-device-naming
Please note that a "debug" (LED_FUNCTION_DEBUG) option already exists if
that is more appropriate to your use-case.
Let's also bring Jacek into the conversion, since I know that he did a
bunch of work around this topic.
The question is if the LED name from the schematics tells anything to
the user of the equipment?
The idea behind LED naming is to facilitate matching the LED class
device name as reported by the system with the LED location on the
equipment.
The LED naming standardization intended to enforce consistent
LED naming, and not allowing to add multiple interchangeable
names like wifi/wlan. It also helps to keep LED name sections order in
accordance with Linux documentation, which before had been often
abused by allowing to assign anything to the now deprecated 'label'
DT property.
You see devicetree changes frequently which change the sysfs path of
existing LEDs, last example I saw today:
https://lore.kernel.org/linux-devicetree/20250513170056.96259-1-didi.debian@xxxxxxxxx/
Consider this change:
led-lan1 {
color = <LED_COLOR_ID_GREEN>;
+ default-state = "off";
function = LED_FUNCTION_LAN;
function-enumerator = <1>;
gpios = <&gpio3 RK_PD6 GPIO_ACTIVE_HIGH>;
+ label = "LAN-1";
So this change was made without understanding how LED naming works,
and without reading LED common bindings [0], which clearly states
that 'label' property is deprecated. It makes no sense to add 'label'
when there are already 'function' and 'color' properties present.
Label takes precedence to keep backwards compatibility.
+ linux,default-trigger = "netdev";
};
Before the sysfs path probably was /sys/class/leds/green:lan-1 and
with the addition of the label property now it's probably
/sys/class/leds/LAN-1 … so it changed. This might break userspace,
which relies on certain sysfs paths, maybe.
The main question is: Is that sysfs path considered to be a stable
interface for accessing a particular LED or not?
It should be stable, but since LED sysfs interface is influenced by
DT implementation, then the responsibility for keeping it stable is on
given dts file maintainer.
I've seen this pattern also the other way round, were an old dts only
has the node name determing the sysfs path, people change the node
name or add color/function properties, gone is the supposedly stable
path.
New idea: what about making this somewhat more flexible and less
suprising by _always_ creating the standardized sysfs entry based on
color/function by default, and let label only create an additional
symlink linking to that?
So in the above example /sys/class/leds/green:lan-1 would be the
canonical name/path of that LED, and /sys/class/leds/LAN-1 would only
be a symlink on it?
IMO it would be cheaper to keep DTS implementation stable.
[0] Documentation/devicetree/bindings/leds/common.yaml
--
Best regards,
Jacek Anaszewski
