Re: [PATCH 22/71] ncr5380: Eliminate selecting state

Finn Thain
2015-11-29T10:25:53Z

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.

> 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.

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.

--

>
> Gr{oetje,eeting}s,
>
> Geert
>