Hi Finn,
On Sun, Nov 29, 2015 at 11:25 AM, Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> wrote:
On Sun, 29 Nov 2015, Geert Uytterhoeven wrote:
This still heavily depends on the processing time spent in
NCR5380_read(). You should never use a value derived from
loops_per_jiffy for a non-empty loop,
Sure but the time-out condition isn't supposed to be precise.
Plus/minus a jiffy is no problem. Plus/minus a second is no good.
If an ISA access takes 8 µs, while the CPU runs at 1 GHz, i.e. 500M loops/s,
the difference will be huge.
as it may take much longer. Always compare with an maximum end time
instead.
That can't work with interrupts disabled, which was the problem I was
trying to solve by use of loops_per_jiffy.
Then you indeed can't use jiffies.
Perhaps you can calibrate an NCR5380_read() loop at driver init time,
and use the calibration value later?
NCR5380_poll_politely() in mainline doesn't work with interrupts disabled
either, hence patch 21.
E.g.:
end = jiffies + 2; /* 1 jiffie + 1 safeguard */
do {
if ((NCR5380_read(reg1) & bit1) == val1)
return 0;
cpu_relax();
} while (time_before(jiffies, end);
And a similar loop for "Busy-wait for up to 20 ms".
Interrupts may be disabled during that loop also. Please refer to (and/or
respond to) patch 21, "ncr5380: Sleep when polling, if possible", in which
these changes were made.
So the above loop may never terminate. Oops...
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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