Re: [PATCH] Add the LED burst trigger

From: Pavel Machek
Date: Fri Dec 27 2013 - 14:37:51 EST


> > Well, this one will be really smaller. And yes, it will make some
> > memory non-swappable, but I believe with triggers and infrastructure
> > for N900 (and similar) it will be worth it.
> Ah yes thats such a major proportion of platforms

I don't know other cellphone hardware in details, but there are 900M
Android devices and multi-colored LEDs are quite common.

> > Plus, it will actually save CPU cycles, and thus significant power.
> All of which will be totally wiped out if you bump all the millions of
> x86 server boxes in the world up by one page of kernel space and cause a
> few disk I/Os

I don't suggest people enable this on PCs/servers. This is useful for
small devices, not for PCs. LED subsystem is not usually used on

> > > little driver but the rest belongs in a library and the library can use
> > > accelerators (of any kind) if available, or even things like lightbulbs
> > > via X10 so you can have the big red light in the control room flash if
> > > the machine dies 8)
> >
> > Well, I'd prefer my cellphone to signal me "you have a message" by
> > flashing blue light, not by dimming lights in the control room ;-).
> Where the cellphone has an offload it makes sense to use it, but in the
> general case userspace is much more flexible. You may not want a flashing
> big red light and a siren but if its in kernel then nobody can have it,
> if it's through a library you can.

Well, library is nicer for sending message to the admin over social
network of the month, while kernel module is better for Arduino-based
USB-connected Turing-complete 3-color led.

Unfortunately, collaboration between GNU and Android worlds ends at
the kernel-userspace barrier, so we are unlikely to end up with one
useful library...

[You are right that we could have done something like lpd and have
library+daemon in the userspace playing the LED patterns. I just
believe that this is easier and better done in kernel.]

(cesky, pictures)
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