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

Geert Uytterhoeven
2015-11-29T09:27:26Z

Hi Finn,

On Thu, Nov 26, 2015 at 11:32 PM, Finn Thain <fthain@telegraphics.com.au> wrote:
>> The timekeeping warning does not appear when all 71 patches are applied.
>> Reverse-bisected it - the warning disappears after:
>> [PATCH 50/71] ncr5380: Change instance->host_lock to hostdata->lock
>>
>
> Makes sense. I think that this should solve the problem:
>
> Index: linux/drivers/scsi/NCR5380.c
> ===================================================================
> --- linux.orig/drivers/scsi/NCR5380.c 2015-11-27 09:21:40.000000000 +1100
> +++ linux/drivers/scsi/NCR5380.c 2015-11-27 09:25:36.000000000 +1100
> @@ -230,7 +230,7 @@ static int NCR5380_poll_politely2(struct
> unsigned long n;
>
> /* Busy-wait for up to 1 jiffy */
> - n = loops_per_jiffy;
> + n = 1 + loops_per_jiffy / 10;
> do {
> if ((NCR5380_read(reg1) & bit1) == val1)
> return 0;

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,
as it may take much longer. Always compare with an maximum end time instead.

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".

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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