linux-kernel - Re: [PATCH] 8139too: move wmb before TX DMA start

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Message-ID: <20081008101558.GH7331@solarflare.com>
Date:	Wed, 8 Oct 2008 11:16:00 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Andreas Oberritter <obi@...uxtv.org>
Cc:	Jeff Garzik <jgarzik@...ox.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] 8139too: move wmb before TX DMA start

Andreas Oberritter wrote:
> From: Andreas Oberritter <obi@...uxtv.org>
> 
> The write barrier should be used before starting a DMA transfer. This fixes
> a problem, where almost all packets received on another machine had garbled
> content. Tested with an RTL8100C on a MIPS machine.
> 
> Signed-off-by: Andreas Oberritter <obi@...uxtv.org>
> 
> diff --git a/drivers/net/8139too.c b/drivers/net/8139too.c
> index 53bd903..44344af 100644
> --- a/drivers/net/8139too.c
> +++ b/drivers/net/8139too.c
> @@ -1716,13 +1716,13 @@ static int rtl8139_start_xmit (struct sk_buff *skb, struct net_device *dev)
>  	}
>  
>  	spin_lock_irqsave(&tp->lock, flags);
> +	wmb();
[...]

All memory barriers need a comment to explain why and what they're doing.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
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