From: David Miller <[email protected]>
Date: Fri, 23 Feb 2007 13:45:05 -0800 (PST)
> While probeing PLL information via radeon_get_pllinfo(), it does a
> "gettimeofday(); do_something(); gettimeofday();" type sequence
> explicitly with interrupts disabled, so ends up with a zero
> measurement which then results in a bunch of divisions by zero.
>
> We should decide whether gettimeofday() can be expected to advance with
> interrupts disabled, or that clocksource_jiffies is simply invalid because
> of this behavior.
Actually, with clocksource based gettimeofday(), radeon built-in cannot
work at all.
The reason is that the clocksource code will not jump over to a
clock source other than clocksource_jiffies until the late initcalls
are run, because of this code:
/* clocksource_done_booting - Called near the end of bootup
*
* Hack to avoid lots of clocksource churn at boot time
*/
static int __init clocksource_done_booting(void)
{
finished_booting = 1;
return 0;
}
late_initcall(clocksource_done_booting);
...
struct clocksource *clocksource_get_next(void)
{
unsigned long flags;
spin_lock_irqsave(&clocksource_lock, flags);
if (next_clocksource && finished_booting) {
curr_clocksource = next_clocksource;
next_clocksource = NULL;
}
spin_unlock_irqrestore(&clocksource_lock, flags);
return curr_clocksource;
}
So even if other clock sources are provided, they'll never show up until
after the radeon driver tries to initialize.
I understand the intention of the clocksource_get_next() code, it doesn't
want to hop onto several different clocksource implementations as the
drivers for those startup, but going through all the module_init() calls
for various drivers without a sane clocksource is just as bad of a problem
and is in fact fatal in this radeon case.
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