On 04/06/2016 10:52 AM, Pavel Machek wrote:
Hi!
Lets say we have
/sys/class/pattern/lp5533::0
/sys/class/pattern/software::0
/sys/class/led/n900::red ; default trigger "lp5533::0:0"
/sys/class/led/n900::green ; default trigger "lp5533::0:1"
/sys/class/led/n900::blue ; default trigger "lp5533::0:2"
Normally, pattern would correspond to one RGB LED. We could have
attribute "/sys/class/pattern/lp5533::0/color" containing R,G,B for
this pattern.
Could you give an example on how to set a color for RGB LED using
this interface? Would it be compatible with LED triggers?
Where the "pattern" class would be implemented?
Well, 'echo "50 60 70" > /sys/class/pattern/lp5533::0/color' should
set the color for the led. 'echo "trigger-name" > trigger' would set
the trigger, probably just toggling between LED off and set color for
the old triggers.
Where to implement the patterns is different question, but for example
drivers/leds/pattern?
I'd rather leave the pattern issue for now, since it seems to be
different from the problem Heiner was trying to solve with his LED RGB
extension. Moreover, hardware patterns are device specific and it could
be hard to propose a generic interface.
Well, RGB leds are basically useless without pattern support. And I
believe we can do generic interface.
Drivers can always expose their custom sysfs attributes for configuring
the patterns.
Regardless of the above, some of your considerations brought me an idea
on how to add generic and backwards compatible support for setting RGB
color at one go.
Currently LED class drivers of RGB LED controllers expose three LED
class devices - one per R, G and B color component. I propose that
such drivers set LED_DEV_CAP_RGB flag for each LED class device they
register. LED core, seeing the flag, would create a generic "color"
sysfs attribute for each of the three LED class devices.
The "color" attribute would contain "R G B" values. Setting the "color"
attribute of any of the three LED class devices would affect brightness
properties (i.e. constituent colors) of the remaining two ones.
It would result in disabling any active triggers and writing all the
three color settings to the RGB LED controller at one go.
Having one attribute across three devices is rather ugly. And we'll
need to solve the pattern issue one day.
What's tricky about patterns is that you need to control 3 (or more)
leds at a time. Problem you are trying to solve here is ... control of
3 leds, at the same time.
So let's solve them together.
OK, now I've got your point. So we'd need to have a means for defining
patterns. The interface could be located at /sys/class/leds/patterns.
We'd need to have a flexible way for defining LED class devices involved
in a pattern. Since we cannot guarantee no space in a LED class device
name, then a single attribute containing space separated list is not an
option. We'd have to create a predefined set of attributes that would
contain LED class device name. Predefined implies that it would be
a fixed number, i.e. either some attributes would always remain unused
or, which is even worse, we could run out of free attributes for some
use cases.
The same constraints would appear if we wanted to be able to define
more than one pattern.
It would be best to work out more flexible solution. I wonder if
ioctl interface isn't the only option.
--
Best regards,
Jacek Anaszewski
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