linux-kernel - Re: [PATCH 2.4.32] Fix AVM C4 ISDN card init problems with newer CPUs

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Date:	Fri, 4 Aug 2006 14:21:55 +0200
From:	Willy Tarreau <w@....eu>
To:	Michael Buesch <mb@...sch.de>
Cc:	Jukka Partanen <jspartanen@...il.com>, kkeil@...e.de,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 2.4.32] Fix AVM C4 ISDN card init problems with newer CPUs

On Fri, Aug 04, 2006 at 12:39:12PM +0200, Michael Buesch wrote:
> On Friday 04 August 2006 08:56, Willy Tarreau wrote:
> > On Thu, Aug 03, 2006 at 06:56:15PM +0100, Alan Cox wrote:
> > > Ar Iau, 2006-08-03 am 19:53 +0300, ysgrifennodd Jukka Partanen:
> > > > AVM C4 ISDN NIC: Add three memory barriers, taken from 2.6.7,
> > > > (they are there in 2.6.17.7 too), to fix module initialization
> > > > problems appearing with at least some newer Celerons and
> > > > Pentium III.
> > > 
> > > Should be using cpu_relax() I think. Its a polled busy loop so you want
> > > other CPU threads to run if possible.
> > 
> > You mean like this ? Here's the patch for 2.6, I'll queue the same for 2.4
> > if it's alright.
> > 
> > > Alan
> > 
> > Regards,
> > Willy
> > 
> > From 512d12bd7ce9c0a15dfd91a6f7c2970c92b3abdd Mon Sep 17 00:00:00 2001
> > From: Willy Tarreau <w@....eu>
> > Date: Fri, 4 Aug 2006 08:50:10 +0200
> > Subject: [PATCH] AVM C4 ISDN card : use cpu_relax() in busy loops
> > 
> > As suggested by Alan, use cpu_relax() in 3 busy loops : "It's a
> > polled busy loop so you want other CPU threads to run if possible".
> > 
> > Signed-off-by: Willy Tarreau <w@....eu>
> > ---
> >  drivers/isdn/hardware/avm/c4.c |    4 ++++
> >  1 files changed, 4 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/isdn/hardware/avm/c4.c b/drivers/isdn/hardware/avm/c4.c
> > index f7253b2..aee278e 100644
> > --- a/drivers/isdn/hardware/avm/c4.c
> > +++ b/drivers/isdn/hardware/avm/c4.c
> > @@ -22,6 +22,7 @@ #include <linux/capi.h>
> >  #include <linux/kernelcapi.h>
> >  #include <linux/init.h>
> >  #include <asm/io.h>
> > +#include <asm/processor.h>
> >  #include <asm/uaccess.h>
> >  #include <linux/netdevice.h>
> >  #include <linux/isdn/capicmd.h>
> > @@ -150,6 +151,7 @@ static inline int wait_for_doorbell(avmc
> >  		if (!time_before(jiffies, stop))
> >  			return -1;
> >  		mb();
> > +		cpu_relax();
> 
> cpu_relax() implies a memory barrier.

OK fine. Reading from various asm-xxx/processor.h files, I was not sure about this.
I will repost it fixed and queue it for next 2.4 too.

> Greetings Michael.

Thanks,
Willy

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