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

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Message-ID: <alpine.LNX.2.00.1511292106140.32336@nippy.intranet>
Date:	Sun, 29 Nov 2015 21:25:53 +1100 (AEDT)
From:	Finn Thain <fthain@...egraphics.com.au>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
cc:	Ondrej Zary <linux@...nbow-software.org>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	Michael Schmitz <schmitzmic@...il.com>,
	Linux/m68k <linux-m68k@...r.kernel.org>,
	scsi <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 22/71] ncr5380: Eliminate selecting state


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
> 
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