On Friday 08 August 2008, Segher Boessenkool wrote:
> > I don't know yet for sure what happens, but a quick look at the commit
> > seems to show that the driver synchronously spin-waits for up to 2.5ms
>
> That's what the comment says, but the code says 2.5 _seconds_:
>
> + /* Wait for up to 2.5 milliseconds */
> + for (i = 0; i < 250000; i++) {
> + if (!(tr32(GRC_RX_CPU_EVENT) & GRC_RX_CPU_DRIVER_EVENT))
> + break;
> + udelay(10);
> + }
>
> (not that milliseconds wouldn't be bad already...)
It can potentially be even much longer, because each udelay will wait
for *more* than 10 microseconds, and tr32() is an mmio read that takes
additional time, possibly in the order of microseconds as well.
The correct way to implement a timeout like this would be to use
time_before() in the condition, aside from better not doing a busy-loop
in the first place.
Arnd <><
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