On 01/25/2017 10:04 PM, Jacek Anaszewski wrote:
On 01/25/2017 10:03 AM, Rafał Miłecki wrote:
On 21 January 2017 at 22:42, Jacek Anaszewski
<jacek.anaszewski@xxxxxxxxx> wrote:
On 01/21/2017 05:24 PM, Rafał Miłecki wrote:
On 20 January 2017 at 23:35, Jacek Anaszewski
<jacek.anaszewski@xxxxxxxxx> wrote:
On 01/20/2017 10:56 PM, Rafał Miłecki wrote:
From: Rafał Miłecki <rafal@xxxxxxxxxx>
Some LEDs can be related to particular devices described in DT. This
property allows specifying such relations. E.g. USB LED should usually
be used to indicate some USB port(s) state.
Signed-off-by: Rafał Miłecki <rafal@xxxxxxxxxx>
---
V2: Replace "usb-ports" with "led-triggers" property which is more generic and
allows specifying other devices as well.
When bindings patch is related to some followup implementation, they usually go
through the same tree.
Greg: this patch is based on top of e64b8cc72bf9 ("DT: leds: Improve examples by
adding some context") from kernel/git/j.anaszewski/linux-leds.git . Is there any
way to solve this dependency issue? Or should this patch wait until 3.11 is
released?
---
Documentation/devicetree/bindings/leds/common.txt | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/Documentation/devicetree/bindings/leds/common.txt b/Documentation/devicetree/bindings/leds/common.txt
index 24b656014089..17632a041196 100644
--- a/Documentation/devicetree/bindings/leds/common.txt
+++ b/Documentation/devicetree/bindings/leds/common.txt
@@ -49,6 +49,17 @@ Optional properties for child nodes:
- panic-indicator : This property specifies that the LED should be used,
if at all possible, as a panic indicator.
+- led-triggers : List of devices that should trigger this LED activity. Some
+ LEDs can be related to a specific device and should somehow
+ indicate its state. E.g. USB 2.0 LED may react to device(s) in
+ a USB 2.0 port(s). Another common example is switch or router
+ with multiple Ethernet ports each of them having its own LED
+ assigned (assuminled-trigger-usbportg they are not hardwired).
+ In such cases this property should contain phandle(s) of
+ related device(s). In many cases LED can be related to more
+ than one device (e.g. one USB LED vs. multiple USB ports) so a
+ list of entries can be specified.
+
This implies that it is possible to define multiple triggers for
a LED class device but it is not supported by LED Trigger core.
There is linux,default-trigger property which allows to define one
trigger that will be initially assigned.
With proposed "led-triggers" property one could assign different
trigger *sources* to a LED. You could e.g. assign 2 USB ports, network
device & CPU to a single LED. For reason explained above Linux
couldn't support all of them at once.
I am aware that this is renamed usb-ports property from v1,
that attempts to address Rob's comment, but we can't do that this way.
Maybe usb-ports property could be documented in led-trigger-usbport's
specific bindings and a reference to it could be added next to the
related entry on the list of the available LED triggers (which is
actually missing) in Documentation/devicetree/bindings/leds/common.txt.
I'm wondering if we need to care about this Linux limitation and if it
should stop us from adding this flexible DT property. Maybe we could
live with Linux having limitation of supporting one trigger type at a
time?
That's what I meant. Generally I have objections to the generic
property for defining list of allowed triggers. That's why I proposed
to stay by usb-ports property that would be specific to only one
trigger: led-trigger-usbport.
led-trigger-usbport in fact is an entirely new type of LED trigger.
LED triggers is a kernel based source of events. All existing triggers
react only to a single, well defined source of events, whereas
led-trigger-usbport allows to define the scope of events (usb ports)
to notify about. Activity on each port is treated similarly and the LED
class device that listens to the trigger notifications doesn't know
which exact port triggered the notification.
From this POV led-trigger-usbport is kind of facade, which allows
for it to fit well into the LED Trigger design and API, and usb ports
are not identical with LED triggers, but sit rather one level below.
It is led-trigger-usbport which is visible to the LED subsystem, and
not every single usb port.
So e.g. if one assigns 2 USB ports + network device + CPU and
decides to use "usport" trigger driver he'll get LED indicating status
of USB ports only.
How would it be different from the current state? Only in limiting
the scope of triggers available for a LED class device.
It won't differ from the current state. I just wanted to make it clear
Linux trigger drivers may respect only selected "led-triggers" values
(phandles). Like "usbport" respecting USB port phandles but ignoring
CPU ones, net ones, etc.
This is the ambiguity I want to avoid. According to my analysis from
the previous message, physical usb port is one level below usbport LED
trigger, and it should be reflected in DT binding documentation. You
can't write usb1-port1 (using the convention from Documentation/leds/
ledtrig-usbport.txt) to the "triggers" sysfs file. You can only register
usbport trigger which can be configured to notify about activity on
usb1-port1.
That's why I proposed linux,trigger-sources name for that.
Let's not confuse LED triggers with events originating from physical
devices or other sources of kernel events, being in turn translated by
LED triggers to LED brightness changes.
This is a thing about naming. It is tempting to call sources of kernel
events "triggers", but they are not LED triggers on they own. LED
trigger is a driver that registers itself in LED Trigger core using
led_trigger_register() API.
Thanks a lot Jacek for this explanation (and sorry but I needed a bit of time to
think about this). I can finally see your point, I think we're on the same page
now.
I think that for all this time I was thinking from the pure DT perspective. If
you ignore fact that Linux has multiple LED trigger drivers, then "led-triggers"
may not sound that bad.
After reading your description however I can see this property can be misleading
as Linux people may think "drivers" when seeing "triggers".
I still think this is a useful property and I hope we can still find a way to
name it in a sane way: to be nice from DT PoV and march Linux LEDs subsystem.
I think we should still work on some generic property (without linux, prefix) as
this seems to be something generic, not really specific to Linux implementation.
Specifying relation between LED and devices is something than AFAICS can be
reused by other systems as well.
So my suggestion is to try some new name & leave linux,default-trigger to allow
specifying one single trigger driver as required by current Linux
implementation.
What do you think about this?
There are few suggestions to came to my mind:
"trigger-sources"
"trigger-devices"
"led-trigger-devices"
"led-related-devices"
"led-event-devices"
Do you think any of them would work? Or can you think of any better name?
