From: Segher Boessenkool <segher@kernel.crashing.org>
To: Scott Wood <scottwood@freescale.com>
Cc: netdev@vger.kernel.org, jgarzik@pobox.com, linuxppc-dev@ozlabs.org
Subject: Re: [PATCH] gianfar: Add I/O barriers when touching buffer descriptor ownership.
Date: Wed, 2 May 2007 02:54:40 +0200 [thread overview]
Message-ID: <65f0b79871a670eb595cca7d78e2f4e9@kernel.crashing.org> (raw)
In-Reply-To: <20070501165542.GA31285@ld0162-tx32.am.freescale.net>
> The hardware must not see that is given ownership of a buffer until it
> is
> completely written, and when the driver receives ownership of a buffer,
> it must ensure that any other reads to the buffer reflect its final
> state. Thus, I/O barriers are added where required.
>
> Without this patch, I have observed GCC reordering the setting of
> bdp->length and bdp->status in gfar_new_skb.
The :::"memory" in the barriers you used prevent GCC
from reordering accesses around the barriers.
AFAICS you need stronger barriers though; {w,r,}mb(),
to prevent _any_ reordering of those memory accesses,
not just the compiler-generated ones.
Segher
next prev parent reply other threads:[~2007-05-02 0:54 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-01 16:55 [PATCH] gianfar: Add I/O barriers when touching buffer descriptor ownership Scott Wood
2007-05-02 0:54 ` Segher Boessenkool [this message]
2007-05-02 16:04 ` Scott Wood
2007-05-02 18:05 ` Segher Boessenkool
-- strict thread matches above, loose matches on Subject: below --
2007-05-16 20:06 Scott Wood
2007-05-18 0:45 ` Jeff Garzik
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