On Thu, Sep 18, 2008 at 18:45, Fundu wrote: >> that book explicitly covers your question. read chapter 2 >> where it >> covers these irq functions. > > as i said i'm reading the book and actully i did read that chapter. > > for me, here's the exact line that needs clarification, > In chapter 2, page 42 last paragraph(starts with "However, if ..." ) > > here's the code snippet he's talking about. > Point A: > local_irq_disable(); > /* critical section ...*/ > local_irq_enable(); > > > Author say, if irg are already disabled at Point A (see snippet above) then local_irq_enable() creates an unpleasant side effect of re-enabling interrupts rather than restoring interrupt state. this was the section i referred to ... but i guess it made perfect sense to me since i'm familiar with the details > 1) first what's the difference between re-enabling and restoring interrupt state. many irq controllers have a global enable bit. you can restore the interrupt mask state without toggling that bit. > 2) so is disable interrupts twice a problem, or just enabling them when after they are diabled (which sounds like how it should be ) a problem. both are a problem. the non-state saving version cannot be used recursively nor in parallel to the state-saving version. -mike -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
