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

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Message-ID: <20060804201429.GA27529@1wt.eu>
Date:	Fri, 4 Aug 2006 22:14:29 +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.
(...)
> cpu_relax() implies a memory barrier.

Ok, here's the updated patch for 2.6 using cpu_relax() instead of
mb(), as suggested by Alan and Michael.

Regards,
Willy

> Greetings Michael.

>From b76136dc1ac989081933d28ec958ecdd32d368e4 Mon Sep 17 00:00:00 2001
From: Willy Tarreau <w@....eu>
Date: Fri, 4 Aug 2006 22:11:23 +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 |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/isdn/hardware/avm/c4.c b/drivers/isdn/hardware/avm/c4.c
index f7253b2..8149dce 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>
@@ -149,7 +150,7 @@ static inline int wait_for_doorbell(avmc
 	while (c4inmeml(card->mbase+DOORBELL) != 0xffffffff) {
 		if (!time_before(jiffies, stop))
 			return -1;
-		mb();
+		cpu_relax();
 	}
 	return 0;
 }
@@ -302,7 +303,7 @@ static void c4_reset(avmcard *card)
 		if (!time_before(jiffies, stop))
 			return;
 		c4outmeml(card->mbase+DOORBELL, DBELL_ADDR);
-		mb();
+		cpu_relax();
 	}
 
 	c4_poke(card, DC21285_ARMCSR_BASE + CHAN_1_CONTROL, 0);
@@ -326,7 +327,7 @@ static int c4_detect(avmcard *card)
 		if (!time_before(jiffies, stop))
 			return 2;
 		c4outmeml(card->mbase+DOORBELL, DBELL_ADDR);
-		mb();
+		cpu_relax();
 	}
 
 	c4_poke(card, DC21285_ARMCSR_BASE + CHAN_1_CONTROL, 0);
-- 
1.4.1

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