[PATCH] Switch leds from mutex to spinlock to work in atomic contexts

Werner Almesberger werner at openmoko.org
Mon Jul 7 14:57:13 CEST 2008

Holger Freyther wrote:
> Switch from using a mutex to spinlock 
> to control the brightnes of the leds...

This is bogus. Spinlocks don't do anything on a uniprocessor - they're
even removed during compilation.

Here are some choices of what you can do if you need to lock something
that can be called from an interrupt:

- move it into a workqueue, so you can use locks that sleep or even
  omit them
- similarly, use a tasklet instead of a lock
- don't lock when in the interrupt code, and protect the non-interupt
  code by disabling interrupts while in the critical section
  (careful about what this does to interrupt latency !)
- in the interrupt, probe the lock and do not perform the action if


- Werner

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