Re: [PATCH 2.4.32] Fix AVM C4 ISDN card init problems with newerCPUs

From: Alan Cox
Date: Fri Aug 04 2006 - 05:42:08 EST

Ar Iau, 2006-08-03 am 19:31 +0200, ysgrifennodd Karsten Keil:
> Yes, that should be go in.
> AVM C4 ISDN NIC: Add three memory barriers, taken from 2.6.7,
> (they are there in too), to fix module initialization
> problems appearing with at least some newer Celerons and
> Pentium III.
> Acked-by: Karsten Keil <kkeil@xxxxxxx>
> Signed-off-by: Jukka Partanen <jspartanen@xxxxxxxxx>

NAK: Alan Cox <alan@xxxxxxxxxx>

Two reasons

#1 You should use cpu_relax in such loops
#2 The readl (which c4inmeml is a pointless #define of) is defined to be
a volatile reference itself

That means that the real bug would appear to be different and either you
have a gcc bug which is possible or you have something stranger going
on, such as the continued polling busying the microcontroller the other
end, in which case you need a delay not the lucky chance that mb() is
slowish on some x86 systems.

So you either want

cpu_relax + other fixes
or udelay(something)


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at