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 12:39:12 +0200
From:	Michael Buesch <mb@...sch.de>
To:	Willy Tarreau <w@....eu>
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 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.

-- 
Greetings Michael.
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