LED blinking during suspend

Lars-Peter Clausen lars at metafoo.de
Wed Dec 16 14:39:14 CET 2009

Hash: SHA1

Werner Almesberger wrote:
> c_c wrote:
>> If I set the LED light on, and suspend the phone - does it stay
>> on automatically - or do I need more magic?
> As far as the hardware is concerned, it will stay on. I'm too lazy
> to check if the kernel will turn it off for you in suspend :)
You need a modified kernel, but it's a one liner. Add
.retain_state_suspended = 1,

to the led struct in arch/arm/mach-gta02.c

>> What about the current consumption?
> About 5 mA per LED. About 50 mA per LED if the LED has the base
> resistor problem. Normal suspend current with GSM on should be
> somewhere around 8 mA, maybe a bit less. So the LED would take a
> considerable bite out of that,
> From a usability point of view, I'm quite sceptical about this idea
> of using a LED as a permanent indicator. LEDs are very limited in
> the amount of information they can signal to a human being, and if
> you have a lot of different states to signal, the patterns may not
> be very intuitive.
> I think it would be interesting to try to find a way for resuming
> the display really quickly, so that one could just bring up the
> screen, check the status indicators for any news, and then send the
> device back to sleep.
Actually it is already pretty fast with a recent kernel and
xf86-video-glamo. I would say about a second.

A led as an indicator that something has happened is imo pretty nice,
because you don't have to press any buttons nor have to really focus
your eyes. And only if it's on you'll turn the device on to see what
actually happened.

- - Lars

> - Werner
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