Messages in this thread | | | Date | Fri, 16 Mar 2012 12:05:20 -0400 | From | "John Stoffel" <> | Subject | Re: Building BarGraph with LED subsystem |
| |
simon> I have a couple of questions about the (user-land) use of the simon> LED subsystem.
simon> I recently offered a patch for controlling the LEDs of the G27 gaming simon> wheel, on which the LEDs are arranged in a bar-graph of 5 to show simon> simulation RPM. The suggestion was to use the LED subsystem, which this simon> patch implements.
simon> http://www.spinics.net/lists/linux-input/msg19747.html
simon> Thinking further about how to about how to control this I was wondering simon> whether a 'threshold' trigger would be useful. This would allow the use of simon> value (uint?) to be compare against a threshold and the LED turned on/off simon> automatically.
simon> The main benefit of doing this as a 'trigger' is that we could 'link' (or simon> 'sync') multiple LEDs to use the same value input, thus making the simon> user-land stuff trivial.
While making the kernel more complex... esp for a feature which is of such limited use. Do it all in userland, it's easier, you can use floating point math, etc. And to test changes, you don't have to recompile a module and unload/reload it, etc.
Keeping as much of this in userland is better.
simon> Also I have a question about the default permissions on the LED simon> controls; Is it possible to register LEDs so that users have simon> write permission? At present the controls are only accessible simon> as root.
udev is the answer here. You probably want to make it so that the LEDs are open to the user logged into the system console or currently active Xsession.
John
| |