Re: [PATCH 1/4] Blackfin: arch patch for 2.6.18

[Aubrey <aubreylee@gmail.com>]

On 9/23/06, Arnd Bergmann <arnd@arndb.de> wrote:
> > +static uint32_t reloc_stack_operate(unsigned int oper, struct module *mod)
> > +{
> > +     uint32_t value;
> > +     switch (oper) {
> > +     case R_add:
> > +             {
> > +                     value =
> > +                         reloc_stack[reloc_stack_tos - 2] +
> > +                         reloc_stack[reloc_stack_tos - 1];
> > +                     reloc_stack_tos -= 2;
> > +                     break;
> > +             }
>
> no need for the curly braces here and below

Hmm, but we need one line < 80 columns, don't we?

> static inline void default_idle(void)
>
> > +{
> > +     while (!need_resched()) {
> > +             leds_switch(LED_OFF);
> > +           __asm__("nop;\n\t \
> > +                         nop;\n\t \
> > +                         nop;\n\t \
> > +                         idle;\n\t": : :"cc");
> > +             leds_switch(LED_ON);
> > +     }
> > +}
> > +
>
> This looks racy. What if you get an interrupt after testing need_resched()
> but before the idle instruction?
>
> Normally, this should look like
>
>         while(!need_resched()) {
>                 local_irq_disable();
>                 if (!need_resched())
>                         asm volatile("idle");
>                 local_irq_enable();
>         }
>
> Of course that only works if your idle instruction wakes up on pending
> interrupts.


No, that doesn't work on blackfin. Blackfin need interrupt(here is
timer interrupt) to wake up the core from IDLE mode. Once you disable
the interrupt, the core will sleep forever.

-Aubrey
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